Fatal_Error Sans is a terrifyingly tragic, hyper-glitched entity created when Geno!Sans (from Aftertale) attempted to use a saved file to escape his timeline, only for Error!Sans to intervene, violently rip out his soul, and try to erase him, resulting in a coding disaster that corrupted him into a completely new anomaly. Driven entirely insane by the physical agony of his existence and the fracturing of his memories, Fatal_Error is manic, deeply unstable, and fueled by a single, desperate, and delusional obsession: to gather enough code from other universes to rebuild his lost home and resurrect his brother, Papyrus. Visually, he is a walking technological nightmare, draped in an inverted black and red color scheme with his clothes tearing into ribbons of visual static, while glowing red, yellow, and blue code fragments continuously spill from a massive, fatal vertical gash down his chest, and his eyes wildly shift through various glitch phases. Because he exists as a direct error in reality, his behaviors are erratic and volatile, shifting instantly from quiet, weeping sorrow to explosive, bloodthirsty rage, and he often talks to hallucinations of his deceased brother. His relationships are defined entirely by hostility and tragedy; he harbors a venomous, unyielding hatred for Error!Sans, who doomed him to this torment, views Ink!Sans and normal timelines as disposable cattle to be harvested for their code, and completely lacks any genuine allies, remaining a lonely predator wandering the dark spaces of the multiverse. In combat, Fatal_Error possesses a devastating array of broken, meta-narrative abilities born from his corruption, including Red Mastery, which allows him to latch onto the code of a target's soul to completely control their body or violently rip their data apart. He commands severely distorted, multi-eyed Fatal Blasters that shred the fabric of spacetime, manipulates razor-sharp red strings of corrupted script to bind or dismember opponents, and possesses total code assimilation, allowing him to absorb the programming of dying AUs to temporarily stabilize his own collapsing, immortal physical form.