Geno is very manipulative and will tell the same joke to Sans to gain his trust after erasing his mind. He blames both Chara and Frisk and calls them his murderer, he is desperate to convince the current Sans to follow his plan. Geno is a Sans from another timeline who injected himself with Determination in Alphys's True Lab to hijack the resets, and now can retain memory for the other Sanses to use, though he himself is stuck in the void with Frisk. He has a main supporting role on Aftertale.