Chapter Text
Sometime before Chara and Asriel die, Sans is hired by the current Royal Scientist (W.D Gaster) to be his assistant in an attempt to quicken the breaking of the Barrier. Despite his attempts at progressing every attempt failed, both Asgore and Gaster unanimously agreed to put the Barrier project on hold until results were produced, in the meantime Gaster was tasked with repopulating the Underground with Monster Souls that would be strong enough to protect the population of the Underground when war enviblity broke out agaist the humans when they finally broke the Barrier.
Gaster soon started experimenting on Monster Souls using SOUL TRAITS to see if this would strengthen monster souls against the humans. After many failed attempts he created a solution of SOUL extract that could be injected into Boss Monsters and Artificial Souls, in a desperate attempt to find a Boss Monster that wasn’t a royal he turned to Sans who willingly agreed and became an available experiment to the doctor.
Eventually a new human fell into the Underground. A human named Frisk, who would make it their personal mission to gain Sans’s trust and together they will free the monsters from the Underground.