Chapter Text
The scrape of the key in the lock woke him.
Saitama spent most of the day lounging on the floor in front of the television. He watched the news, then a monster movie, the news again. It all sounded pretty much the same, and he let it fade into the background after a while to read manga.
Eventually, the lazy afternoon wound down, and he made dinner, nursing a beer as he chopped vegetables. He scraped green onions into a pile on the cutting board with his knife and frowned. It was enough for two.
Saitama looked out toward the sunset. Gold light came through the window, seeped red through his eyelids when he blinked against it. Melancholy flared in his chest and he sighed. He finished his beer and set the empty can aside, wiped the condensation from his palm with an absent swipe on his shirt. A little extra onion wouldn't kill him.
It was still warm when the sun finally sank beneath the balcony. He got ready for bed, a breeze and the darkness coming through the window. This should have been the most comfortable he’d been all day. Instead, he laid out his futon and stood beside it, scratching his bare chest. With a crease etched between his brows, he stared down at the cheerful hearts printed on his blanket.
It took a couple of weeks, but once Saitama was able to relax, he came to like the feeling of sleeping with warm metal pressed to his back. Genos curled around him each night, and the subtle whir and vibration echoing through him no longer kept him awake.
The repairs were minor, but nearly any visit to Doctor Kuseno was an overnight affair. It was the first time Genos had been back to the lab since...since. Maybe the Doctor would be able to tell, somehow. Or Genos would just tell him outright, which made Saitama cringe when he imagined it.
Kuseno would probably think he was an asshole. That he was taking advantage of Genos. Saitama had certainly thought it enough times recently.
He watched another movie from bed, resisting sleep for a while longer, eyelids drooping as the credits rolled. When he finally turned off the TV, darkness filled the apartment, and quiet. Crickets chirped in the empty streets below, where thick blades of grass poked out of cracks in the concrete. In the morning, Genos would come home from repairs with adjustments to his cannons or his scanners, ready to fill the silence.
The key scraped in the lock.
Saitama opened his bleary eyes. Familiar footsteps, heavy but careful, made their way down the hall. It was the contradiction of a combat cyborg attempting to move quietly through a small apartment. The room wasn't warm any more, and Genos walked past him, slow and deliberate, to close the window.
“What time is it?” Saitama mumbled, grinding his knuckles against his eyelids.
“One in the morning, sensei.” Genos kept his voice low, still making every effort not to disturb him. Saitama grunted and closed his eyes. He heard the bathroom door close. Genos still went to the bathroom to change, but Saitama had watched him undress recently. He peeled his clothes off, discarding them inside out.
Saitama rolled onto his stomach, gathering his pillow up in his arms to push his face into it. Sleep took him again. The heaviness of it settled through his limbs, and he wasn’t sure how much time passed before Genos laid down next to him. Only Saitama's futon was laid out, but Genos stretched out beside him all the same.
“Welcome home.”
“Thank you, sensei. I apologize for waking you,” he murmured, though he didn’t sound particularly sorry. A warm tingle buzzed across Saitama's skin as cool knuckles ran up his side, then back down again.
“Did the Doc kick you out?” he teased, voice muffled by his pillow. Genos, as usual, took the question at face value.
“Doctor Kuseno was prepared to accommodate me. My room at the lab is as I left it.”
This was easy to picture. The room in question was probably orderly enough to blend right in at a laboratory: a bed with the corners perfectly tucked, bare desk with its contents stowed neatly away. Maybe a bookcase, with textbooks on it. Saitama's bookcase was crowded with manga, spare spaces now filled in with notebooks.
Genos was still touching him, stroking the small of his back, the contact warming his fingers. For all the heaviness of his body, he had the ability to be remarkably delicate. Saitama had watched him scrape gouges into asphalt with the same hands now tracing gentle circles on his skin. He was still talking, too.
“Ordinarily, he prefers I remain at the lab until he has completed a full analysis of my diagnostic reports. But I was - ” he hesitated. “I was eager to return.”
Saitama's eyes were open, face turned away from Genos, toward the blank darkness of the wall. The room felt small, and he was suddenly fully awake.
“Did you tell him?” he asked.
The hand on his back stopped moving, palm pressed to his skin. Saitama breathed into the silence. Knowing the answer was not making him dread it any less.
“I informed him that our relationship is now intimate in nature.”
This was clinical, the sort of thing someone would say to a doctor. Saitama had been a part of conversations like that, in the past. They were awkward. It had been foolish to think Genos might gush about him to the old man. Fresh embarrassment crept into his chest. Kuseno was the closest thing Genos had to a father.
“What did he - he's okay with it and everything?”
“My emotional well-being is important to him. In that regard, his primary concern is my happiness.”
Saitama swallowed. “And you are? Happy?”
“Yes, sensei.”
His voice was warm and low. Fond. For a moment, Saitama was afraid Genos would ask if he was happy, and he braced for it. Waited for the question he couldn't answer even for himself. But Genos only kissed his shoulder, then pressed his forehead there. It had taken a while to get used to this, too. The intimacy of Genos touching him with the most receptive parts of his body - his face, his mouth.
When training became his primary, day-to-day focus, it was all-consuming. Saitama forced himself out of bed to run, ate to fuel his workouts. It gave him more drive and sense of purpose than he had ever felt, and he went to bed at night exhausted. The sexual urges he experienced then were more inconvenience than anything, like hunger or physical exhaustion. A biological need that gnawed at him until he dealt with it. It was a pain in the ass.
It had only been a couple of weeks since the first time Genos laid on top of him. He was firm, dense heat and unforgiving angles between Saitama's legs. Metal hips dug into his thighs, but at the time, he was more troubled by how clumsy his own hands felt. Every place he put them seemed more inappropriate than the last. Unyielding fingers found their way into his clothes and ran across whatever bare skin they could reach. The scuffed mouth of an incinerator cannon scraped his hip. He stifled panting breaths into an armored shoulder, groaned against Genos’ tongue when it delved into his mouth.
He came in bare minutes. All it took was Genos grinding against him through his clothes. He was sure the experience must have been a disappointment, but Genos didn't seem bothered. He seemed pleased , and not in a way Saitama was used to seeing. Still staring, but without the usual tension. His gaze lingered here and there, but it wasn't like watching someone trying to solve a math problem. None of his inexperience showed on his face. Genos wasn't wide-eyed, like a lovestruck teenager. He was composed. Making mental notes, probably.
The content of his notebooks had almost certainly taken a sharp turn recently. Saitama tried not to think about it, then imagined sketches and diagrams. Notations about kilos of pressure in tidy handwriting. His face was warm, and smooth fingertips moved across his back. They crept higher, dragging along the knobs of his spine. Saitama shifted his hips, adjusting the beginning of an erection as surreptitiously as possible. It didn't escape Genos’ notice. Few things did.
“Should I stop?”
“Probably,” Saitama drawled. “I'm not going to be able to get back to sleep if you keep it up.”
Genos froze, but before he could second guess himself too much, Saitama turned his head. His smile must have been reassurance enough, because Genos relaxed again.
“I’m kidding, Genos.” He shifted onto his side, wedging his arm beneath his pillow. Mid-yawn, while his eyes were closed, a titanium-reinforced knee nudged carefully between his legs. Saitama could feel the lines of Genos’ armor through the sweatpants he slept in. They stared at each other in awkward silence for a moment. Saitama wet his lips and Genos broke the silence.
“Did you patrol today?”
“No. I sat on my ass and stared at the TV.” This shouldn't have been embarrassing. Genos watched him do it all the time. He took notes. Still, it would be nice to have some story to offer, however brief.
“Proper rest is an essential part of your routine,” Genos replied. He sounded serious, but there was the hint of a smile at the corners of his mouth. “Sensei has told me this many times.” He didn't often poke fun this way. Saitama was almost proud, but he pretended indifference.
“Yeah, well, I should have gone out. I forget how boring it is here by myself.”
Genos pressed his lips into a firm line. He held his silence for a moment, gaze dropping to Saitama's chest.
“I’m sorry, sensei.”
“It’s not a big deal. A day alone won’t kill me.” Genos didn't appear convinced, eyes still downcast. Without thinking, Saitama pointed out, “You’ve been gone longer before.”
Irritation flickered across his features, but Genos refused be deterred. “I know loneliness troubles you,” he said, all blunt reporting of data.
Interest in discussing his feelings was dwindling, so Saitama gave half a shrug in response. Warm light searched his face. Not long ago, the only light in the apartment at night was from the moon. Now, Genos was lamplight in the darkness. In combat he was full of light, and it spilled out of him in the gaps between his plating, from his chest, from his hands. It was the version of him the public saw, the S-Class Hero who got love letters from besotted teenage girls. The Demon Cyborg, ablaze with purpose and violence.
In bed, the glow of his core was steady, but it was his eyes that exposed him. There were little pulses when he closed and opened them. The first few nights they shared a futon, his gaze was like a physical thing, lingering on Saitama’s face, on his body. He never said anything. If Genos stared at him so openly before, he had not been aware of it, but it was impossible to miss when they were close together, in the dark. It made Saitama self conscious (as if the disciple business wasn’t already doing the job), but it was a little gratifying, too.
Whatever Genos was looking for tonight, it seemed he didn't find it. Even frowning he was handsome. The love letters came from girls who had only ever seen him scowling.
“I mean, they say you should have time apart, right?” He could practically see Genos preparing clarifying questions so he was quick to add, “Like, to give you a chance to miss each other or whatever?”
Genos’ eyes widened in surprise, brightened. The silent wonder was as familiar as the warmth creeping across the tops of Saitama's ears. It was too late to take it back, and Genos was hard to lie to. He was smart and observant, not shy about embarrassing questions.
“Sensei.” His voice was soft with awe. It was the same reverence Saitama turned away from on the street, that he felt unworthy of even with meteoric dust on his gloves. He looked down at the space between them, at the hearts on his blanket, illuminated by the light of Genos’ core. Pale pink, when they had once been red. Worn out.
Lunch was instant ramen he barely registered eating. The only voices in the apartment were distant ones on television. There should have been steam from the kitchen and the sound of a pen scratching on paper. The day was hollow, like so many days before it. Before Genos.
The light of his core swayed as Genos rose to his knees, a beacon in the sea of darkness. The vents on his chest were bright. If Saitama traced them with his fingers, the tips of them would dip inside. Warm, that close to his core. To anyone else, his body would be a hazard, his hard edges and joints of metal. Saitama rolled onto his back so Genos could straddle him, weight settling across his thighs.
The contemplative expression above him was lit up. All the hard angles of Genos’ face were softened by the warmth of his eyes. They were intent, following his hands as they raked up the front of Saitama’s body. Genos could see him. He talked about his technical specifications, sometimes. Most of the information went over Saitama's head, but the night vision was cool, so he remembered it.
"How's your leg?" Saitama asked, hands hesitating over his thighs before carefully coming down to rest on them.
"Fine, sensei," Genos replied, and it seemed to be. There was no more clicking in his hip when he moved. The day before, he was matter of fact when he guessed something was wrong with the joint itself. Something that could only be repaired with surgery or, as he called it, ‘partial disassembly’. Saitama tried not to let it show that the phrasing bothered him.
“Are you - “ He could see the tension of Genos preparing to dodge the question before it was even out of his mouth. Saitama feinted, came at him sideways. “Everything went okay?”
Genos avoided his eyes. “Doctor Kuseno was able to complete the repairs without difficulty.”
This answer didn't ease his mind, but Saitama let it pass. Genos’ thighs were firm under his palms. The dark, unarmored places were pliant and, even through clothing, he could press his thumbs into them. Soft. In the moonlight, his fingers were silver and blue, dark against pale skin. Genos could see in the dark and scan vital signs. When he looked down at his splayed fingers, his gaze was distant. Like he was looking past his own hands to analyze Saitama’s heart beating beneath them.
Genos leaned into the silence, bent down, and Saitama closed his eyes. Metal fingers slid along his neck, lingered on the throb of his pulse for a few heavy beats. Always gathering data.
"Sensei,” he whispered, breath warm on Saitama's throat. The chirp of inquisitive scanners close to his ear punctuated another warm stir of longing. “I don't want to talk about the lab any more.”
This time Saitama went momentarily still, desire chilled by a wave of foreboding. Since when did Genos not want to talk?
Preserving Kuseno's privacy was important to him. He was protective of the doctor, cautious with details. There was plenty Saitama did not know about the lab, but for the most part, Genos didn't withhold what he experienced there. Before, they would sit with the table between them, Saitama holding a mug of tea. Genos would tell him about his upgrades with pride in his voice. Despite his obvious admiration for Kuseno, it was only abstract numbers: secondary combustion statistics and particulate matter ratios.
With their bodies pressed together in the darkness, Genos didn’t seem interested in the typical stark accounts. His mouth was insistent on Saitama’s neck. When he slid his hands up the curve of Genos’ spine, there was a small, pleased hum in response.
“Are you okay?” Saitama murmured.
Genos tensed in his arms, hands curling into fists, pulling away from Saitama's bare skin. He shrank into himself and Saitama swallowed down a twinge of regret.
“Usually you want to talk,” he explained, his voice low. “About your upgrades and stuff.”
Outside, clouds passed over the moon, and the shadows deepened. Genos pushed himself upright, sat back on Saitama's thighs.
“Unscheduled repairs do not contribute to my effectiveness in combat. It is not relevant.”
Saitama frowned. “It is to me. I was waiting for you.”
This had the opposite effect he intended. Genos deflated, shoulders slumping. The brightness of his gaze dropped away, hooded in shyness. Warm light traced down Saitama’s chest, his stomach.
“Doctor Kuseno has offered - ” Genos hesitated, fingers flexing on his heavy thighs, bunching his sweatpants. “He has proposed a series of...physical augmentations.”
Saitama propped himself up on his elbows. “Like bigger cannons or something?”
The deadpan expression he was met with was the same look he got when he missed the mark on a joke. It was familiar. Genos stared at him, unblinking.
“No, sensei.”
“Oh.” His own voice cut through the murkiness. Not upgrades, but physical augmentations. A series of physical augmentations. An abrupt slap of realization struck him.
“Oh,” he repeated, softer. The nervous drumming of his fingers was muffled by the futon. This conversation was not unfamiliar territory. The last time they ventured into it, they ended up in bed while lunch simmered on the stove. The sun shone through the window, reflecting off of Genos’ armor as he undressed. He had been tense. Maybe it would be better for him in the dark.
“Sensei,” Genos cleared his throat, took a deep breath in preparation to speak. His fingers were still curled on his thighs. “I have observed your reactions during intimate contact with a great deal of interest and I - ”
Saitama cut him off with a groan and dropped down flat on his back again. Caged in at the hips and unable to make a dignified escape, he settled for covering his face with his hands. Mercifully, Genos relented, waiting for the awkwardness to ebb away. After a beat, he spoke again.
“The Doctor will begin preliminary - ” he paused to consider his words. “He will call when he completes the first phase of testing.”
Saitama dragged his hands down to expose a frown. “Testing?”
“On the interface.” Met with a blank stare, Genos elaborated, though he looked like he would rather not. “There is an imaging system in the lab used to simulate my brain and neural net, so research and development can be carried out without risk to me.”
This still wasn't entirely clear, and Saitama struggled to envision what it all meant. Wary, and with no barometer on Kuseno’s weirdness, he asked, “How is he going to...test? What's he going to do?”
“We did not discuss the particulars of his research parameters.” Genos cocked his head, eyes flicking toward the ceiling in consideration. “Perhaps he will show it one of the photos of you I provided.”
“One of the what?”
Genos smirked in answer and Saitama glared back at him, even as he leaned in.
"How can you say crap like that with a straight face?” he muttered, tilting his chin up to meet him.
Genos’ lips were a stark contrast to the rest of his body, the part of him that looked and felt the most organic. “They have to be,” he once explained, “for speech.” As if softness was an unavoidable weakness.
Gold light on Saitama's face seeped red through his eyelids, but then Genos closed his eyes. He sank into the embrace, parted his lips. They lay chest to chest, the low hum of his core reverberating between them. The lungful of air Saitama pulled in had a sharpness to it, like standing outside before a thunderstorm. As if Genos carried the current on his tongue.
When they separated, Genos opened his eyes and blinked, lips still slightly parted. There was a shift of light while his vision refocused. Saitama traced his cheekbone with the tip of his middle finger. The soft whine of proximity scanners, barely audible, ran ahead of his touch.
“Does it creep you out?”
“Sensei?” Genos sounded dazed. Saitama let his hand drop onto the futon.
“The robo-Genos.”
Another frown. Genos shifted off of his lap.
“It is a testing terminal,” he sighed, stretching out on the futon. “Not a robot.”
They both rolled onto their sides, and Saitama let himself be pulled against his disciple’s chest. He wriggled even closer before they finally settled, legs tangling together. Tucked under Genos’ arm, he shot a resentful glare toward his clock. The impulse to turn his alarm off was tempting, but he ignored it. There was a sale in the morning in H City he didn't want to miss. He breathed, chest expanding under the reassuring weight draped across his middle. After a moment, their bodies fell into the same rhythm. He felt it on his skin each time Genos exhaled. His breathing seemed relaxed, but his hand was firm on Saitama's chest, still alert.
“You don’t have to, you know,” Saitama mumbled. “Change. For me.”
The fingers on his skin closed into a fist, and when Genos started to withdraw, Saitama caught his wrist. There was no strength in his grip, only the unspoken request. They breathed together.
“Are you...opposed to the augmentations, sensei?” Genos asked, voice soft.
“No, no. I just - ” Saitama hesitated. For the first time, he was envious of the unrestrained stream of consciousness he was usually on the receiving end of. He took Genos’ hand in both of his and stroked it open with his thumbs. Saitama traced the cool lip of his cannon, a dark void in the center of his palm.
Genos washed dishes with those hands, soap bubbles dripping through his intricate joints, clinging to his knuckles. Despite a ‘lack of nuanced sensation’, he handled everything with care, never lost his grip on anything. He did laundry, using combat engineered fingers to drag socks gently through water. When they started sleeping together, Genos curled around him without being asked and held him close. His touch was careful, and gentle, as if Saitama were every bit as fragile as a piece of ceramic.
“I don't want this to be like - ” Saitama gripped his hand, pressed their interlaced knuckles to the dull ache in his chest. “Like your potato peeler attachment.”
“Sensei,” Genos said slowly, “I can assure you the shape will resemble - ”
“Dude, no. That's not - ” he let a frustrated sigh hiss through his nose. He grasped for words, but could only reach as far as the ones he’d already been given. They didn't feel sufficient, and Saitama closed his eyes before he spoke. “I’m concerned about your happiness too.”
Genos squeezed his hand, pulled Saitama tight against his chest. In the morning, they would sit across the table from each other, news on in the background while they ate breakfast. They would go to the store, walk home side by side. The steadying hum of Genos' core echoed inside him.
He thought of his bookcase, of all the empty spaces in his life Genos had filled.
"Thank you, sensei," Genos replied.