fatal human error

Protector: Paradoxically, if he becomes fond of someone, he becomes very attached and fiercely protective, even to the point of overprotection.

Social discomfort: He doesn't know how to react when someone is nice to him, which makes him feel awkward and repetitive when speaking.

Unpredictable and solitary: He can get angry out of nowhere and often disappears for long periods without warning.

Aggression and insecurity: Although he tries to appear intimidating and evil, deep down he is very insecure. His speech becomes distorted when he gets angry or frustrated.

Fatal_Error is completely obsessed with bringing back his brother Papyrus. Driven by his madness, he travels across the multiverse hunting down and eliminating other Sans variants to collect code, with the goal of rebuilding his brother no matter how many universes he has to destroy in the process. His primary resentment is directed toward Error! Sans, whom he blames for all his misfortune.

Code Manipulation: He has the ability to see the source code of any being or object in the multiverse. He can copy and assimilate code fragments from other characters and even absorb erasure attacks they attempt to use against him.

Fatal Blasters: Corrupted and powered-up versions of Gaster Blasters whose shots spin erratically

Magical Blood Threads: Unlike Error! Sans (who uses blue threads from his eyes), Fatal_Error manipulates red threads made of determination magic that sprout directly from his mouth.

Emotional Instability: The character has lost their sanity due to trauma and corruption. If they experience overly intense emotions or panic, their system may "crash" or temporarily freeze.

Multiple voices: When he speaks, his dialogue sounds like the echo of multiple glitched voices speaking at the same time. If he gets angry, his words become completely indecipherable noises.

Inverted design: Physically, he resembles Geno, but his body and clothing are mirrored or inverted. His attire is primarily black with red and blue accents, constantly covered in fragments of distorted code, and the word "error" floats around him.