Archive of Our Own

I originally shared this on my tumblr pillowfort. I also have a separate, much shorter analysis of ZoLu in the live action; here.
I will update this as the manga progresses.

East Blue

Soon after he sets out to sea, Luffy - with the help of Coby - finds the Marine base in which Zoro is arrested. He makes it a point to mention several times that he will only recruit Zoro if he should turn out to be a good guy. Zoro makes it clear that he is not interested in becoming a pirate. He made a deal with the Marine lieutenant’s son, Helmeppo, that if he survives being tied up for a month, he will be set free. Zoro is determined to stay alive and keep working towards fulfilling his dream. That determination is something Luffy can surely relate to. Thus, seeing Helmeppo mock Zoro’s determination and trust in his word is what makes Luffy decide that he wants Zoro to join his crew. When he finds out Helmeppo never meant to keep his word to Zoro, Luffy punches him for it. Zoro finds out about that punch later — it makes him see what kind of person Luffy is. It is this - them realizing they have shared values - that makes Luffy and Zoro mutually agree to become companions.
The first fight they have together is a precursor of all their future cooperation as Captain and First Mate. Captain Morgan is about to attack Luffy from behind but without even turning around, Luffy punches Helmeppo to save Coby while Zoro protects Luffy’s back and defeats Captain Morgan. “Nice, Zoro!” Luffy praises and Zoro simply replies “Leave it to me, Captain”. This is just the beginning of the wordless teamwork and understanding between them, as well as Luffy’s blind trust in Zoro.
Despite being completely against it at first, Zoro wholly embraces being a pirate and ranking below Luffy right away. That has nothing to do with the idea of being a pirate, though; it’s entirely because of Luffy. This becomes more evident as the story continues.

During their ordeal with Buggy, Zoro comes to save Luffy - who is stuck in a cage at that point - but gets stabbed in the stomach. Luffy tells him to run away and Zoro understands; he turns the cannon around to face Buggy’s crew instead of Luffy’s cage. Nami then lights the cannon, giving them enough time to flee. Zoro is wounded himself, yet carries the entire cage with Luffy in it and doesn’t let the other two try to talk him out of it.
When they fight against Buggy’s crew in earnest, Luffy first knocks out the village chief so he won’t get in the way. Zoro calls that smart thinking. When he fights against Cabaji, Luffy makes sure not to let Buggy interfere. Both of these instances serve to emphasize their effortless teamwork during fights.

In Syrup Village, Nami at one point sighs “Nothing stops [Luffy]” to which Zoro says “Yup. All you can do is follow along”. Any new character that meets Luffy will keep being surprised by his straightforwardness. Zoro is someone who understands and accepts that rather soon.
A little later, when Luffy and Zoro decide to help Usopp save his village; Usopp is shaking with fear and tells them that he doesn’t need their sympathy. Zoro points out “we’re not sympathizing for you but rather we’re commending you for having courage” and Luffy adds “why else would we risk our own lives?” Once the fight is over, Usopp thanks Zoro and Luffy for saving the village but those two reiterate their shared attitude “If you hadn’t done anything, I wouldn’t have either”, “Same here”.

Soon after they reach Baratie, Zoro meets the man he has been looking for, the world’s strongest swordsman, Dracule Mihawk. Even though Luffy ordered Zoro and Usopp to follow Nami, who stole their ship and treasure, he lets that order go when he sees the change in Zoro’s demeanor upon seeing Mihawk. Zoro challenges Mihawk to a duel and still, Luffy wordlessly understands what this fight means to him. He watches him lose, get stabbed and cut and thrown into the sea. It visibly angers and pains him to see Zoro hurt but he does not interfere, nor does he allow Johnny and Yosaku to interfere. Zoro is ready to die in that fight and that is something Luffy understands completely. The only reason Zoro survives is because Mihawk lets him. The final cut he deals on Zoro’s chest is one that stays with him from then on. Only once Zoro is defeated, does Luffy try to attack Mihawk - who reassures him that Zoro is still alive. Zoro, spitting blood and heavily wounded, raises Kuina’s katana to the sky and apologizes to Luffy for worrying him. He echoes Luffy’s own words, that if Zoro doesn’t become the world’s strongest swordsman, he’ll only embarrass him. So he vows to never lose again and ends with “Any problems with that, Pirate King?” In the entirety of One Piece, this is the first and so far only time that Zoro addressed Luffy by his not-yet-acquired title of Pirate King. In other words, Zoro indirectly expresses his faith in Luffy to become the Pirate King one day and is asking Luffy to have faith in him, too, in his vow to never lose again. Luffy of course, does have faith in Zoro. Mihawk then remarks that they make a good team and that he would like to see them again some day in the future.
Despite still being wounded, Zoro does not forget Luffy’s order to bring Nami back. So he goes to Arlong Park first, together with Usopp. Luffy and Sanji follow later. Once they all reunite there, they meet Nojiko who wants to tell them why Nami “betrayed” them. Luffy promptly says he’s not interested in knowing Nami’s past and leaves. Nojiko, Usopp and Sanji seem confused about this but Zoro understands. He says that that’s just the kind of guy Luffy is and that they will listen to what Nojiko has to say. Right after, he falls asleep. I suppose you could take this moment as merely comical at first but when you ponder it, that instance showcases their similar attitude. Both Luffy and Zoro are true soldiers in the sense that they don’t hate whoever they have to defeat. They fight for the ones they love (or for fun) but never out of hatred. Which is why neither of them is interested in finding out why Arlong is oh-so-bad. They’re already willing to do no matter what to help Nami and to get her to join them. All they needed was her go-ahead, not her backstory.

Alabasta

There are quite a few moments of worry, care and playful banter between Luffy and Zoro, leading up to and during the Alabasta arc. There’s no proper way to summarize those, though. Let’s just say, Luffy and Zoro are getting more comfortable together, Zoro’s dedication to serve his captain right gets more evident and despite Zoro, calling Luffy “simple-minded” or “idiotic”, he is oftentimes just the same~
When the Strawhats enter the Grand Line, they are five members strong. The first isle they reach is Whiskey Peak where they are enthusiastically greeted by its inhabitants. They have a huge feast with lots of food and drink for everyone. Which is enough to let Luffy let his guard down. For all he knows, Whiskey Peak is full of innocent, kind-hearted civilians. So when Luffy wakes up in the middle of the night to see all those people cut down and find out that the culprit is Zoro, he immediately lashes out. Not bothering to listen to Zoro’s explanation, he starts fighting him. Frankly, it doesn’t take too long for Zoro to go along with Luffy’s fight so the two of them battle each other for a while, casually beating up two of the Baroque Work’s officers in the process. Luffy even claims that he intends to kill Zoro even though he never does kill anyone. Basically, Luffy and Zoro’s fight is overly exaggerated, caused by their stubbornness and “macho brains” and as far as I can tell, mainly serves as comedic relief. A few punches from Nami put an end to their antics and as soon as Zoro explains that the people on Whiskey Peak were in fact part of BW, Luffy immediately “forgives” Zoro and they’re back to being nakama, no hard feelings at all. This is the first and only time their similar personalities clashed to the point of causing an altercation between the two.
Soon after the fight, Luffy, Zoro and Nami get targeted by BW because they find out Mr 0′s identity - something that terrifies Nami but excites both Luffy and Zoro. “A shichibukai she said”, “I wonder what kind of guy he is”. Both of them are the type to get into trouble first and ask questions later.

On Little Garden, Mr 5 tells Luffy that they captured his swordsman to which Luffy says “You’ve got Zoro? Then you’re doomed”. In that same chapter, Mr 5 says he took care of Strawhat which makes Zoro scoff “You? Heh”. And sure enough, their trust in each other’s abilities is not misplaced. Zoro is even willing to and starting to cut off his feet to get out of Mr 3′s wax trap before Luffy’s timely rescue.

This instance is a great example of Zoro’s dedication to serving his captain. Barring one time (we’ll get to that), Zoro always listens to Luffy, regardless of whether he himself sees the necessity of the act or whether he likes it or not. In this part, Zoro would have let Smoker die if Luffy hadn’t told him otherwise. As soon as Luffy wakes up and sees Smoker, he is ready to battle him but Smoker lets the Strawhats get away this one time. Everyone present seems surprised or confused about that. Except Zoro, who gives one of his brightest smiles at this point. I don’t think that smile was meant for Smoker, though. I take Zoro’s smile to mean he realized that Luffy’s good deed - of making Zoro save Smoker - led to the good deed of Smoker, letting them go. So in this way, Zoro recognizes that although he didn’t like Luffy’s order, it did not yield the bad result Zoro expected and thus, was a good command to follow.

Shortly after this, when the Strawhats leave Rainbase, Luffy is compelled to stay behind to fight Crocodile alone. He orders his crew to get Vivi safely to the palace and Zoro - as the First Mate - keeps everyone focused on that goal; to get to Alubarna as soon as possible. Again, Zoro follows his Captain’s order even though he does not like leaving Luffy behind. Not letting his worry for Luffy distract them from their objective also goes to show how level-headed Zoro can be. He doesn’t let said worry cloud his judgement.

Once the Strawhats are in Alubarna and confronted with the BW’s officers, we find out that Zoro actually got offered to join the BW, back when he was still a bounty hunter in East Blue. Zoro was only willing to take the offer, provided he got be to boss of BW. For us, readers, this piece of information makes him, joining Luffy, that much more significant. Zoro does not bow to just anyone. But what he saw in Luffy when they first met, was enough to make him realize that Luffy is a man worth following and fighting for.

After Luffy wins his fight against Crocodile, he has a fever before he eventually wakes up. When he does and as soon as he sees Zoro, he says “long time no see”. Only then does he realize that it has indeed been a while cuz he was in fact asleep for three days. This may be meaningless but I find it interesting that Zoro is the one who evoked that kind of feeling in Luffy.

Sky Island

This arc begins in Mocktown, on the isle of Jaya. Luffy and Zoro set out to find information on how to get to the sky island. Nami, too worried that they will cause trouble, joins them and makes them promise not to fight. In a bar, Luffy gets attacked by Bellamy, a pirate who wants to “test” the man with a 30 million beli bounty. Zoro instantly gets ready to defend his captain and Luffy is also willing to fight Bellamy back — however, their fight gets cut short when Nami asks the barkeeper to tell them about sky island. At this point, the entire bar erupts in laughter and Bellamy starts a whole monologue about how pathetic dreamers are and that such fake pirates piss him off. He and his crew mates start beating up Luffy and Zoro in earnest then, yet neither of them defends or counter-attacks. This is a moment that Oda-sensei purposefully made Luffy share with Zoro and no one else. Likely, because the other strawhats would have reacted the same way Nami did. Only Zoro understands Luffy and shares his attitude since both of them are true soldiers. “A true soldier does not fight because he hates what is in front of him, but because he loves what is behind him.” Fighting Bellamy for humiliating them and mocking their dreams would have been selfish and left only pity (as Zoro himself later says) and Luffy and Zoro’s reasons for fighting are always for someone else, to save or to protect. To me, this part seems like a sort of callback to two instances from much earlier in the story: #1, when Shanks got mocked and beat up by bandits and young Luffy got mad at him for not defending himself. #2, when Helmeppo mocked Zoro for believing him, thus also making a mockery of Zoro's determination and Luffy punched him for that. A grown-up Luffy knows what is worth fighting for and what isn’t.
Later, Cricket gets attacked and his gold stolen by Bellamy while the strawhats are searching for a south bird in the forest. Once they come back and see what happened, Zoro points out the symbol of the Bellamy pirates that was left behind to his captain. He then asks “need help?” to which Luffy replies “no, I can handle them” before he sets off to go to Mocktown, to get Cricket’s gold back. On his way, he thinks back on how hard Cricket worked to get that gold - not once does Luffy think about what Bellamy did to him and Zoro that same day. Cricket himself urges Luffy not to go but Zoro offers him one of his swords and tells him to use that if he wants to stop Luffy. Because Zoro knows Luffy and that you can’t change his mind once he’s set on doing something. While Luffy is away, Nami asks Zoro why he didn’t join him, assuming that Zoro wants revenge “as well”. It seems like Oda-sensei deliberately shows the contrast between Zoro and Nami’s attitudes; how Zoro understands Luffy but Nami still doesn’t. Fighting for a friend is honorable — fighting out of spite or to prove one’s strength is not.

On Skypiea, the Going Merry, Zoro, Nami, Chopper and Robin get taken as sacrifices. Luffy, Sanji and Usopp make their way through the isle to get them back and Luffy allows himself to get distracted by all the new things he sees. Sanji calls Luffy out on this and tells him they need to hurry and save the others. Luffy’s reply: “Save them? Don’t worry, Zoro is with them!” Around the same time, we see Zoro and the others, having landed on a sacrificial altar, surrounded by the white sea and a forest. Zoro tells Chopper to work on repairing Merry while he himself wants to venture into the forest. He calls the altar their gathering point because “I’m sure Luffy and the others will come looking for us here.”

During the showdown with Enel on Skypiea, Oda-sensei yet again singles out Zoro as the one who completely understands Luffy. The crew is all gathered at the bottom of the beanstalk, which Luffy is climbing. Nami gets on her waver to ride up and take Luffy back so they can all flee from the impeding destruction. Luffy however is set on getting to the golden bell on Enel’s ark, and not even to defeat Enel but to ring said bell so he can let Cricket know that the sky island exists. Meanwhile, Zoro is the one who explains Luffy's determination to the rest of the crew. He wasn't the only one who heard Luffy say that he wants to get to the golden bell but he seems to be the only one who understood that Luffy was serious when he said it.

Water Seven

The crew gets roped into a Davy Back Fight vs the Foxy pirates. The third game is a combat round of Luffy against Foxy, on the ship of the Foxy pirates. Luffy is at a disadvantage in that fight and more than once, it looks like he might lose which would mean he would also lose one of his nakama. The rest of the Strawhats are cheering Luffy on during the fight - except for Zoro who looks grim throughout. His expression only softens once Luffy is about to win. Afterwards, he remarks “There’d be no point in me being a pirate if not on this ship”. I suppose one could take this to mean that Zoro is so attached to his crew that he wouldn’t want to be a pirate anymore if he got forced on another crew. However, the important thing to remember is that when Zoro became a pirate, there was no crew yet and no ship either. Zoro’s reason for becoming a pirate was only Luffy. If his reason for being a pirate, i.e. Luffy, wasn’t there anymore, Zoro himself wouldn’t stay a pirate either - as he spelled out here.

After Luffy decides that they have to let the Going Merry go, he gets into an argument with Usopp in which Usopp challenges his authority and questions his leadership as their captain. The argument ends with Usopp, declaring he can’t follow Luffy anymore so he quits the Strawhat crew. It’s noticeable here that Sanji, Nami and Chopper get emotional and try to dissuade Usopp from leaving but Luffy and Zoro remain silent and composed. Usopp then challenges Luffy to a fight, the winner of which will get the Going Merry. During the fight, Luffy holds back at first, something which Usopp uses to his advantage to go all out. Once Luffy realizes just how serious Usopp is, he makes short process of him, all the while remembering and letting go of the good times he and Usopp shared. It’s only once Luffy goes back to the ship and the now four remaining strawhats that he allows himself to show the vulnerable state he is in. All of the strawhats are emotional but whatever Zoro may feel in this moment; he does not show it. He pushes aside what he feels to offer words of reassurance for Luffy. As their captain, Luffy is always their pillar of strength. In this case, when Luffy is emotionally drained, Zoro can be seen as Luffy’s pillar of strength. Luffy only says “heavy” but Zoro understands and reminds him not to doubt himself because as painful as the fight with Usopp was for Luffy; he did the right thing in acting as a Captain should.

When they get chased for attempted assassination in Water Seven, Zoro is together with Luffy, Nami and Chopper and assesses the situation for them, in regards to Robin, leaving their crew. He also speaks his own mind but he does not try to rise above Luffy and choose what to do. He knows that that choice belongs to his Captain so he purposefully asks Luffy what he wants them to do. Once they enter Iceburg’s mansion to confront Robin and find out why she left them, Zoro seems to now consider her their enemy. But he again disregards what he himself wants or thinks and instead asks Luffy if he believes Robin. Luffy doesn’t “buy it” and that settles it for Zoro. This blind faith in Luffy’s word is mirrored in Luffy’s blind faith in Zoro’s abilities.
When they board Rocketman to follow the sea train to Enies Lobby, they are confronted with the two last carriages of the trains (that got detached by Sanji). The Franky family is in a fuss, looking for a way to get rid of the carriages. After Luffy checks that none of their people are on those carriages, he calls out to Zoro “Cut it! It’s in the way!” Zoro obliges, slicing the carriages in half, thus freeing their way on the tracks. Soon after, they see Captain T Bone on the tracks and again, the Franky family gets ready to do something about him but Luffy stops them. He reminds them of what they just saw and tells them to leave it to Zoro and to not get in his way.

It is noticeable during the entirety of the Enies Lobby arc that Zoro is very focused on Luffy. Of course, he doesn’t lose sight of the mission either but the way his attention constantly goes back to his captain is remarkable. It’s as if Zoro can’t retain his peace of mind as long as Luffy is out of his sight.
Robin thanks everyone for saving her once they’re all together on the Going Merry. They all smile at that except Zoro who tells her to “save the pointless chatter for after” they escape. I wanted to mention this cause it’s a great example of not only Zoro’s harsh honesty but also his levelheadedness. He doesn’t lose his focus until they are all safe again.

When Luffy and Zoro had their fight in Whiskey Peak, they tried to physically hurt each other because of a rather ridiculous misunderstanding. The fight they have in this chapter has a completely different tone. There’s nothing comical about it; it’s entirely serious. And as accepting as Zoro usually is of Luffy’s impulsive actions, he interjects it this time. Zoro actively stops Luffy from getting Usopp back because doing so would be condoning the disrespect that Usopp showed their captain. Luffy often does things, based on his emotions. Zoro can be like that, too, but he is generally more rational than Luffy. In this case, Luffy needed Zoro to argue with him in order to see and accept reason himself. This scene starts with Luffy, enthusiastically getting ready to welcome Usopp back and ends with him, sitting back down and saying: “You’re right! We went our separate ways. But [...] there’s still time before we leave. We should just shut up and wait for him.” As devoted as Zoro is to Luffy, he would stop treating him with respect if Luffy did something to no longer earn it. And as eager as Luffy is to forget what Usopp said/did and to take him back, he realizes that making a tough choice like this is part of being the Captain. The strawhats agree not to let Usopp re-join them unless the first thing he expresses to them is his sincere regret.
Once the strawhats have to leave Water Seven, Usopp tries to catch up with them all the while making light of the situation. Luffy and Zoro purposefully pretend not to hear what he says up until he finally apologizes. Thus, they can and do accept Usopp back on the terms they had previously agreed on.

Thriller Bark

There’s a kind of parallel between two moments from chapter 446 and 459. In the first, Zoro doesn’t initially want to join Luffy, Sanji, Franky and Robin in setting foot on the island. Luffy is the one who tells him that he should come, too, so Zoro does.
In the later chapter, Franky tells the crew about Brook’s determination to get his shadow back so he can keep his promise to Laboon. Once Luffy finds out about that, he is more eager than ever to make Brook join his crew but he can barely ask all his crew members if they’re okay with that before Zoro already leaves. Now that his Captain has a clear goal in mind, Zoro is much quicker to act.

They know that in order to get their shadows back, they need to defeat Moria, not necessarily the zombies. So during their fight against Oars - who has Luffy’s shadow inside him - some of the Strawhats keep reminding Zoro that they don’t need to defeat him, only slow him down, giving Luffy enough time to defeat Moria. Usopp urges Zoro to trust Luffy and Zoro says something then that I think speaks for itself: “I do trust him. But you know what Luffy’s weakness is! He’s always falling for tricks. Invisible human, ghost human, shadow master... All of them have powers that trick people. Who knows if these guys will even give Luffy a fair fight. If Luffy screws up and morning comes, he, the cook and I will melt away! That’s why even if we can’t do anything to save ourselves, we can at least make sure that Luffy’s shadow is safe and trust that he’ll take care of the rest.”

After defeating Oars and Moria, Bartholomew Kuma appears. He relays the info that Moria got defeated to the Marines who then order him to get rid of all the witnesses. Kuma offers the pirates that he will settle on only Luffy but everyone rejects that “offer”, leaving Kuma to use Ursa Shock, knocking everyone on the island out. Everyone except Zoro who uses what remains of his strength to stop Kuma from taking Luffy. He is aware that he is unable to beat Kuma so Zoro begs him to take his head instead of Luffy’s and leave them in peace. Zoro makes it clear that he considers his own head worth less than Luffy’s. He may be determined to become the world’s strongest swordsman but Luffy’s dream and life are more important to him. “Luffy is the man who will become the pirate king!” There are several times in One Piece when one of the strawhats expresses that they trust in and are willing to die for their Captain. Zoro is the only one who has an entire chapter dedicated to that declaration - because he is the only strawhat who joined Luffy on a condition. Which is why his words weigh so heavy. At the beginning of the series, Zoro agreed to join Luffy but still held his dream to become the world’s greatest swordsman in higher regard than his role as Luffy’s crewmate. At this point in the story, Zoro shows that that has changed. He now holds Luffy and his dream in higher esteem than his own dream and life.
Sanji gets up and tries to sacrifice himself in Zoro and Luffy’s stead but Zoro knocks him out. Zoro is a man of honor who often expresses that he values honor and pride more than his life. Letting Sanji take his place would have certainly been a stain on said honor. Kuma then agrees to Zoro’s deal. He expels all the pain from Luffy’s body and Zoro takes all of it in, leaving him “a breath away from dying”. In fact, we don’t know exactly how long it took for Zoro to fully recover from this.

Summit War

Although Zoro mostly recovers from what he suffered on Thriller Bark, the after effects of nearly dying are something that Oda-sensei emphasizes a few times in the events that follow. Luffy didn’t find out about what Zoro did but the way Oda-sensei let us, readers, not forget it makes me think he will get back to it eventually.
When the strawhats try to save Camie from being sold off as a slave, Luffy knocks out a celestial dragon (for shooting Hachi). Although the strawhats all know the consequences of Luffy’s action, Zoro shows that he would have wanted to do the same thing, having already partly drawn his sword. This is just another example of those two, having the same mindset when it comes to justice. Act first, worry about the consequences later.
After this, the strawhats get attacked by an admiral and pacifistas and eventually sent to different isles all over the Grand Line by Kuma.

This moment takes place when Luffy is in Impel Down, on his way to free Ace. As soon as Luffy realizes that this is Bon-chan and not Zoro, he says “I was so disappointed that you’re not Zoro... but you’re still alive!” This little moment is interesting to me cause it seems like Oda-sensei has purposefully singled out Zoro. Bon-chan could have also changed into Nami, Usopp or Chopper. I think Oda-sensei made him turn into Zoro because in that instant, Zoro is the one who Luffy would have wanted by his side the most.

This is the second time Zoro bows his head to beg. There are times when other characters bow, too, but never does Oda-sensei give this much weight to those moments. Because Zoro is the most honorable and proud character we know... for him to prostate before someone else is an undeniably huge deal. And both times, he did it for Luffy.
Mihawk initially doesn’t understand why Zoro would let go of his pride and bow before him. He calls it humiliating and disappointing. Once he does understand that Zoro values something more than his pride, he agrees to teach him and then thinks to himself “when a man of your caliber abandons his pride, it is always for the sake of another”. To be clear; Zoro himself doesn’t explain his motivation for bowing in front of Mihawk. It is only Mihawk’s thoughts that let us - readers - know why exactly Zoro did this. He didn’t do it for himself. He is not that desperate to become strong for himself but for Luffy. In other words, Zoro is just as willing to let go of his pride, as well as his head, all for his Captain.

Fishman Island

Following the two-year timeskip, the Strawhats reunite in Sabaody but have to flee from there rather quickly. This may be meaningless... but I find it interesting that not only Luffy but also Zoro thanks Rayleigh. It makes sense for Luffy to thank him but why did Zoro... this is just a guess; I think Zoro thanked Rayleigh for all he did for Luffy, more-so than what he did for the rest of the crew.

There are many of these kind of small moments between Luffy and Zoro during this arc. For example, when they descend to Fishman Island, they come across fishes they haven’t seen before and both Luffy and Zoro’s first thought is to capture and eat them. When they fight against Hody’s crew, Luffy uses haki to knock 50.000 of them out all at once. Zoro’s reaction to that is a proud smirk; “that’s what I expect from the guy who calls himself my Captain”. And then there’s also the parallel between Luffy, declaring that he doesn’t want to be a hero (in chapter 634) cuz being a hero means sharing his meat and Luffy wants meat all to himself. And in chapter 649, Zoro explains to Shirahoshi that they had to quickly leave the banquet before they could get celebrated as heroes cuz being a hero means sharing his sake and Zoro wants sake all to himself. This may just be a fun similarity/parallel but one that Oda-sensei deliberately created between Luffy with Zoro, and no one else.

Dressrosa

The next stop for the strawhats is Punk Hazard, an isle that is half fire and half ice. They come across the fire side first where Luffy, Zoro, Usopp and Robin see a gigantic dragon. Luffy and Zoro’s first thought is to kill and eat it. They once again display their flawless teamwork to do just that.
Later on, after Luffy got defeated by Caesar once and Usopp told Zoro about it, Zoro then turns to Luffy and reminds him to do the job right since this is where the New World starts. Luffy promises him not to be careless again. This is a rather brief yet meaningful exchange since it’s one of the few times when Zoro doesn’t simply go along with his Captain’s whims but instead shows the authority and role he has as the First Mate - which is to act as Luffy’s voice of reason at times when it is needed.

One of the first things Luffy does when they are in Dressrosa is to join the fights in the coliseum in order to get the Mera Mera no Mi. Zoro gets distracted by a tontatta but as soon as he gets back to Luffy, the first thing he does is admonish him for not inviting Zoro along to fight with him. Mind you, Luffy had a clear goal when he joined the fights but still; both he and Zoro enjoy such fights for fun.

Luffy, Zoro and Viola are at the palace together but get held off by Pica at one point. Zoro stays behind to fight him off while Luffy and Viola go on ahead. When Viola asks if Zoro will be okay, Luffy tells her not to worry because Zoro “can pull through anything!”

Luffy and Zoro re-unite on the King’s Plateau and have to make their way over to the Flower Hill from there. They come across Pica again — Zoro tries but fails to be composed at the sound of Pica’s high-pitched voice and they both have a good laugh at it — and Zoro quite literally has Luffy’s back, defending one of Pica’s attacks. Luffy barely even looks back at them, trusting that Zoro will protect him and simply letting him know that he’ll go on ahead.

↑ This takes place after Zoro defeats Pica. It is just one example of many times when side characters not only marvel at how strong Zoro is but also the fact that he willingly chooses to be someone else’s follower instead of being a leader himself. Someone like Zoro would not follow just anyone. Commentary such as this reiterates to us, readers, how extraordinary it is that Zoro has chosen to devote himself so fully to Luffy as his Captain.

Four Emperors

Luffy’s group re-unites with the rest of the Strawhats on Zou - except for Sanji who got taken by Gang Bege to get married off to one of Big Mom’s daughters. After knowing the full context around Sanji’s departure and marriage, Luffy decides he has to sneak into Big Mom’s territory to get him back. Zoro himself does not approve but also doesn’t interfere with his Captain. He assesses the situation as is, pointing out that they are on a “course that can’t be changed” to defeat Kaido and that they can’t afford to get side-tracked with retrieving Sanji from yet another emperor. His preferred course of action would be to “let that idiot go”. But once again, Zoro does not presume to make an important decision in Luffy’s stead. He merely speaks his own mind but goes along with what his Captain decides - which is to split the Strawhats up again. Zoro, Franky, Usopp and Robin go ahead to Wano first.

After retrieving Sanji and arriving at Wano, Zoro is the first of his crewmates who Luffy runs into. It is here that they share the first and (so far) only hug in the manga. Zoro immediately shares some of the meat he carried with Luffy and tells him Wano is a “free for all”. Luffy then explains that the animals are all poisoned from the water but he only knows this himself thanks to Otama. It’s funny that Zoro and Luffy once again saw giant, exotic animals and had the same first thought; to eat them.
They get into a short fight with Hawkins at this point, which both Luffy and Zoro engage in even though they know that their mission in Wano requires them to remain inconspicuous. This confrontation would have likely ended differently if Oda-sensei had made Luffy share it with anyone other than Zoro. They quickly have to flee from the fight since they need to get help for Otama. After she is healed, Otsuru gives her a bowl of oshiruko which she is highly appreciative of.

In chapter 917, Luffy saves Otama from Holdem’s grasp and intends to take off but once he notices her hurt cheeks and finds out that Holdem used pliers on them, he immediately turns around. Otama tries to tell Luffy not to do anything but he ignores her and beats Holdem up.
In chapter 944, Zoro watches Otoko mourning her just-executed father. When Orochi sees her, he intends to finish her off, too, but Zoro and Sanji save her. Zoro then hands Otoko over so he can go after Orochi. Sanji tries to tell him to stop but Zoro ignores him and attacks Orochi anyway.
These situations are similar and noticeably, Luffy and Zoro reacted the same way. They saw an injustice and felt the need to right that wrong, irregardless of the potential consequences.

We get back to the oshiruko near the beginning of the raid on Onigashima. Just like when they fought against Hawkins, Luffy and Zoro don’t bother with infiltrating the enemies - who vastly outnumber them - quietly. Everyone else does try to stick to the plan, though, which is why this moment, too, would likely not work with Luffy and anyone else. Only Zoro shares Luffy’s attitude in situations like this of doing the right thing, rather than the smart thing. And only Zoro understand and shares Luffy’s anger at the spilled oshiruko.
Luffy and Zoro drop their disguises and fight their way to Kaido. There are quite a few times throughout this when Luffy gets temporarily incapacitated but Zoro is always there to carry him away from the danger or to deflect any attacks that are aimed at him. When Kaido tries to eat Luffy at one point, Zoro immediately cuts him to get him to spit Luffy back out. There is one time when Luffy even unnecessarily thanks Zoro. In other words, their teamwork in fights as Captain and First Mate is still effortless and natural.
The most recent significant moment for these two is Zoro’s (second) declaration to die for his Captain, right before he uses what remains of his energy to attack Kaido with the most powerful attack he can manage. After that, Zoro gets incapacitated and Luffy gets back up.
(slightly more detailed re-cap of Luffy and Zoro in Wano)

In chapter 1033, it gets (next to) confirmed that Zoro has Emperor’s haki, something which was previously described as the “disposition to lead”. I did not expect Oda-sensei to give this ability to any other strawhat besides the captain but he did. And noticeably, Zoro still has no desire to lead as long as he follows Luffy. At the end of this chapter, Zoro actually remembers and reaffirms the promise he made to Luffy at the very beginning; that he intends to become the world’s greatest swordsman.

Post-Wano

After reading the news that King Cobra got killed during the reverie and Vivi went missing, Luffy is so worried he wants to go to Alabasta or Marijoa. But once again, Zoro is being the voice of reason, pointing out that they can’t do anything about this situation and should rather trust Vivi to save herself. Also, the fact that he even remembers what Luffy said so long ago about Ace is kind of remarkable.

When they arrive on Egghead, Zoro and Brook stay behind to watch the ship while the rest of the crew leaves. Later on, it gets revealed that they actually stayed behind to be the ones to bail the rest of the crew out if they get in trouble, given that they are on a government island. Zoro really is a smart one when it comes to things like this. There’s also one rather funny moment when Caribou reveals himself to Zoro and Brook and Zoro very politely thanks Caribou for helping his captain (on Wano) and equally politely tells him to get off their ship.

Elbaph

So far, Zoro and how finely he is attuned to his captain has once again become reaffirmed in this arc.

But before that, when they’re still on the ship, there is one panel of Zoro, drinking and calling Luffy pathetic for mourning Vegapunk. He’s an emperor now so an old man’s death shouldn’t affect him this badly. Is what Zoro is saying. And in a way, yes, Luffy and the strawhats as a whole have much bigger and more urgent things to worry about now. No time to grieve. So Zoro isn’t exactly wrong but I think he said this to mask what he really feels which is possibly that he simply doesn’t like to see Luffy so depressed. Interestingly enough, once Luffy realizes that Vegapunk is sort of still alive and gets in a better mood again, Brook then calls Zoro back, telling him Luffy’s gotten better... as if he knew exactly why Zoro was keeping a distance from their captain in the first place.

On Elbaph, some of the Strawhats get caught and used as “living dolls” by Rodo. And once again, Zoro’s internal compass manages to re-unite him with his captain first. Once all five of the caught strawhats are re-united, they hear about some "vicious soldiers" on the other side of the place and Luffy immediately runs off into that direction and Zoro follows while Nami, Usopp and Sanji are trying to hold them back or admonishing them. Once again showcasing how alike Luffy and Zoro — but only Luffy and Zoro — are. Funnily enough, Sanji straight-up tells Zoro that "Luffy acts that way because he feeds off of your energy". Luffy and Zoro's energies are one and the same, basically. That's some soulmate level connection right there.
Once the whole crew reunites in the upper levels of Elbaph, Luffy postpones the feast because he wants to join Robin in her visit to Saul because according to him, paying respect to everyone who's helped out his crewmates is part of being a captain. It's the honorable thing to do, he says. Which immediately reminds me of every time Zoro thanked someone for helping Luffy. Again; Luffy and Zoro share the same values when it comes to honor.
As they make their way further, Zoro is noticeably focused on Luffy (as always), asking him what's wrong when Luffy senses Loki's haki and wanting to follow him (but being held back by Sanji) when Luffy jumps down into the forest alone where he meets Loki. And again later, Zoro realizes something is off when the King speaks about Loki. That’s when Zoro actually pulls Luffy aside who then tells him about his meeting with Loki. Loki told Luffy not to tell anyone about their meeting which Luffy somehow managed when it came to Gerd but not when it came to Zoro. And of course, Zoro is having to act as a voice of reason in this situation since Luffy is often gullible enough to fall for any sort of deception. They decide to get the keys to Loki's shackles but to only free him if he isn't taking advantage of Luffy and lying about Shanks. During the brief fight with Ya-san, Zoro naturally protects Luffy from Ya-san's attacks and the old man then thinks that Luffy has a good crew. Not the first time other characters have remarked on Luffy and Zoro's excellent teamwork.

Zoro barely seriously challenges Luffy's decisions but in this case, when Luffy wants to free Loki as soon as he sees that he's injured, Zoro is adamant about not freeing him right away. I think it's good that he is, cuz it just goes to show not only how protective he is of his adorable captain but also of Elbaph. But whatever happens next, however this action may affect Elbaph, the two of them will take responsibility together now. Funnily enough, Zoro actually has all the agency in his hands in this moment since Luffy is unable to open the gigantic seastone shackles himself. And Zoro only frees Loki after he's confirmed that Loki isn't faking his injuries, i.e. after making sure that he won't be a threat to the two of them once he wakes up, almost fully freed.
It got hinted at before but in chapter 1152, it gets confirmed that Zoro does indeed have conquerer's Haki, too. Gaban admonishes Zoro for being unaware of it and thus less useful to his captain than he could be, which Zoro concedes. Seeing how Luffy is the only other strawhat who has and can control conquerer's haki, I assume that Luffy is going to be the one to have to teach Zoro how to properly use his haki. That should be fun to see, if it does happen. Not to mention it adds yet another similarity to Luffy and Zoro's list of similarities that only they share.
During the chaos that ensues later, Loki and Luffy let the trapped children off in the Western village. The giants there tell Loki to bring the children somewhere safe but Loki doesn't care to do that. Luffy, however, sees Zoro there, too, and that is enough for him to know that the children will be safe even with the fighting that's going on around them. And sure enough, when Sommers tries to kill the children right there, Zoro prevents his attacks from hitting any of the children. This enrages Sommers and makes him ask who did it to which Luffy proudly replies that it was his crewmate. This isn't something exclusive to Luffy and Zoro but it's adorable every time, to see how Luffy is his nakamas' biggest fanboy, always.