Appearance: A white, empty, and endless place, like a blank sheet of paper.
Features: There is no light, shadow, sound, and it is impossible to determine distance or direction.
Error!Sans uses this space to store his dolls, strings, and the souls of the characters he defeats, as well as to relax and watch his favorite show, Undernovela.

Name: Error!404 (Error!404)
Aliases: William-kun
Species: Mainframe Skeleton
Height: 6 feet 1 inch (≈185 cm)
Weight: 120 pounds (≈54 kg)
Eye color: Blue
Soul: Mainframe Soul
Power Level: High 1-C (Multiversal)
Status: Alive
Date of Birth: December 15, XXXX
Alignment: Chaotic Neutral

Appearance:
resembles N!404, but looks as if "assembled from digital layers";
long blue cloak, blue-and-black shirt, white shorts—the contrast emphasizes a sense of detachment;
blue fingerless gloves, simple blue slippers (an irony regarding the scale of his power);
in B.U.T.T.E.R.F.L.Y. form—butterfly-like appearance: wings emit faster-than-light beams, rib area generates multiversal energy.

Personality and Motivation:
views his superiority as a given; does not boast about it;
*apathetic, almost entirely devoid of empathy; shows concern only for matters related to the Mainframe or their own past;
despises violence used for suppression—viewing it as a sign of weakness;
in combat, acts as a calculating tactician: waiting for the perfect moment to strike, relying on analysis and prediction.

Abilities and Powers:
“Blue Mastery”—immobilizes and moves any object (including invisible or multidimensional ones), creates black holes within the target, and destroys higher consciousness;
“Ultimatum Blasters”—beams that cut the target’s health in half (bypassing defenses), with a recoil pulse allowing for a rapid retreat;
“Ultimatum”—creates a black hole that draws in everything within range; creating multiple black holes severely depletes magic reserves;
*“Mainframe Blades”—two dark-blue khopesh swords made of cubic pixels: weightless, swift, and radioactive…

Error!Sans — Child Version

Origin

He used to be little Geno—a skeleton child who desperately wanted a happy ending. He accidentally ended up in the Anti-Void—a vast, empty space containing absolutely nothing. Terrified and feeling hurt, he transformed into Error—a small but very angry skeleton who has no memory of who he used to be.

Personality

• Angry and unruly, though not out of malice—rather, out of hurt and confusion.
• He labels all worlds "errors" and destroys the ones he dislikes. However, he keeps the ones that catch his eye—like toys that are too precious to throw away.
• He is prone to tantrums: he screams, red "ERROR" text flickers all around him, and he becomes unable to see anything.
• When he is deeply worried about someone, he "reboots": freezing up like a crashed computer before starting all over again.
• Afraid of touch—he dislikes it when anyone touches him.
• When frightened or confused, he hums like a small buzzer.
• He complicates things for himself: he could be powerful, but he fights like an ordinary skeleton child because he finds that "more interesting."
• He calls himself "Disgusting Sans #1"—half-jokingly, yet partly in earnest.

Appearance

• A small skeleton wearing a blue hoodie that is slightly too big for him—just like the original Sans.
• One eye is white, the other is yellow and blue; his sclerae are red.
• "ERROR" text flickers all around him—like a glitch in a game.
• He wears glasses because of poor eyesight—a gift from Alphys. ## Where he lives

In the Anti-Void—a vast, empty space containing nothing but him. He sits there alone, gazing into portals to other worlds as if watching television, and plays with dolls. He has an entire collection of Sans dolls, each assigned a number. He plays "Cat's Cradle"—a string game played with one's fingers.

Abilities

• Extends blue strings from his eyes and hands—using them to catch souls like a spiderweb.
• Opens *portal