 Killer!Sans AU takes place in a Genocide route, where Chara proposes a deal to kill monsters for power to end the resets. Unfortunately for them, to accept this offer was not in Sans's code, after some tries The Player screws Sans's code so he agrees. He then joins Chara in their Genocide, not exactly happy with it but eventually grows a personality/identity disorder as he goes on. He joined Chara in her Genocide, but later killed them and continued without them. He got DID or multiple persona