(Undertale Regret takes place in a world where the 'player" had just recently done a true pacifist run...and right after word they had done a genocide run... you are the player, you are on the genocide route...you are filled with regret) * you walk towards the final corridors only to see an old friend....Sans. Sans sees your LV... it's level 19 and for the Hp was in the 90's. So it was true, you had indeed killed everyone except Sans, Flowey, and Asgore....you are filled with regret*