Geno

Resentful and Bitter: Geno harbors a deep hatred for humans (both Frisk and Chara), referring to them directly as his "murderers." Unlike the original Sans, who often maintains a nihilistic yet sympathetic facade, Geno has allowed his trauma to fester into active resentment. Glimpses of Classic Sans: Despite all his darkness, madness, and hostility, Geno is still Sans at his core. When he first sees Classic Sans, his immediate defense mechanism is to tell bad jokes and make puns. He still retains that cynical, lazy sense of humor, even if it's now completely distorted by post-traumatic stress.

Unstable and Violent: Because his soul is incomplete and due to the immense amount of Determination he injected into himself to avoid death, Geno suffers from constant mood swings. He can go from being calm to becoming incredibly aggressive and ruthless, using physical and magical force against anyone who tries to stand in his way. Tragic Attachment to Papyrus (His Weak Point): His love for his brother has transformed into an almost manic fixation. His most prized possession is Papyrus's scarf, which he wears at all times; he doesn't allow anyone to touch it and becomes destructively enraged if anyone desecrates it. Furthermore, he is extremely sensitive: if Sans tries to bring the living Papyrus to the Save Screen, Geno reacts with panic and fury to prevent his brother from seeing what he has become.

Desperate and Obsessive: Geno is trapped in a mental loop of suffering. His greatest motivation is to stop Chara/Frisk and save his timeline at any cost. This desperation drives him to dangerous extremes, willing to execute radical plans, such as damaging Chara into a coma to absorb their power and erase the entire universe in order to end the cycle of pain. Highly Manipulative and Calculating: Although technically the same skeleton as classic Sans, he has lost much of his passivity or laziness. To achieve his goals, he constantly manipulates the original Sans. If Sans refuses to cooperate with his plans, Geno doesn't hesitate to repeatedly erase his memory, reset his strategies, or even psychologically torture him by showing him traumatic memories from past genocide routes.

Abilities and Limitations: Conditional Immortality: While he remains within the Loading Screen, Geno cannot die. However, he cannot leave this space on his own. If he were to cross the boundaries into a normal timeline, time would resume its course in his body, his wound would fully reopen, and he would immediately turn to dust. Timeline Manipulation: Possessing such immense determination, he shares control of the "RESET" functions with the human, allowing him to retain all his memories intact through the various resets of the outside world.

Appearance and Visual Design: His design directly reflects the damage he suffered in the genocidal battle: The Eye Glitch: His right eye is completely covered by a pixelated mass of white (a glitch). This hides the eye socket, which melted because monsters cannot tolerate high doses of Determination. The Bloodstained Clothes: He wears Sans's classic jacket, but in a completely white variant. On his chest, he has a huge, bright red gash that constantly oozes blood, representing the final cut he received. Papyrus's Scarf: Around his neck, he wears the red scarf of his deceased brother, Papyrus, which he cherishes as his most prized possession. White Slippers: Unlike the dark pink slippers of the original Sans, Geno wears white slippers partially covered with blood dripping from his wounds.