An epic psychological horror take of the game's universe, a typical genocide route of Undertale is abruptly extended by Sans miraculously surviving his death blow and preventing the player from completing the game and resetting. What follows is Sans's feeble attempts to cope with his trauma from almost dying, to seeing everybody he liked be killed, to being stalked for weeks by an ever-more desperate murderer, leading him down a dark, malignant path of constant delusional reaffirmations, and corrupted illusions spurred by his gradual development of a cancerous SOUL trait which feasts off of his growing natural DETERMINATION, 'MADNESS'. His psychosis eventually spirals into mass murder after he witnesses other humans fall into the Underground overtime, only interrupted after a peculiar, equally afflicted Kindness girl, Rose breaks his expectations and worldview, and attempts to get to the bottom of his inner turmoil, eventually gaining his unstable trust. This leads him to eventually defeat his worst enemy and through their power gain the ability to break out of his own world, exploring a grander, hostile Multiverse which he seeks to eradicate all humans from, for their evil.