Context : It was actually an exact copy of Undertale until that Sans, before becoming Determination Sans, killed everyone without hesitation or complaint, then gave all that Determination to Kris and Chara. Then, thanks to the effects or aftereffects of one of the machines of the former royal scientist Gaster, he absorbed them both and then battled Flowey until he left Flowey's lifeless body in a lake thawed by the impacts. He then returned to the laboratory and used the same machine to absorb and consume even more pure Determination power, amplifying what he had already absorbed and stolen from everyone, thus creating a perfect fusion or combination of pure Determination that changed him internally, but only slightly in his outward appearance. After all these events in that timeline, which was going to be another genocidal act by Frisk and Chara, Determination Sans absorbed everyone else and destroyed his universe, corrupting the code so that it would permanently and irreversibly damage itself. he did.