Ink became a baby because of a killer's joke

Appearance
Killer Sans looks like classic Sans, but with a number of distinctive features:
Clothes: a jacket of a more gray shade with fur on the cream-colored hood, white shorts with black stripes, boots instead of slippers.
Soul: in the center of the chest there is a red circle, resembling a target.
Eyes: Black liquid flows out of his eye sockets, symbolizing his determination.
Pupils: In some versions, barely noticeable pupils may appear in the eye sockets, which is associated with internal psychological changes.
History and background
In this universe, Sans, after multiple resets of the Genocide Path, gradually loses himself. Chara, manipulating him, offers him a deal: join them in the genocide to escape the boredom and despair of endless cycles. At first, Sans resists, but under pressure and the realization that nothing can change, he agrees.
The key moment is the murder of his brother, Papyrus. This event becomes a turning point: it leaves Sans with a profound sense of guilt, which is exacerbated by the ongoing reboots. Over time, Sans's soul merges with Chara's, transforming him into a being who is neither human nor monster.
Killer Sans later realizes he no longer needs Chara and kills them. He later joins the Bad Sanses and becomes one of Nightmare Sans's most loyal subordinates.

Appearance
Ink is a skeletal monster. His bones beneath his clothes are adorned with strange patterns.
Some details of his appearance:
Eyes. Typically, there's a blue circle in the right socket and a star in the left. Their shape and color change when they blink. Each combination is believed to symbolize a separate AU, the events of which they oversee.
Cheek. On the right cheek there is a black spot, reminiscent of mascara.
Clothing: A white long-sleeved T-shirt with a small brown jacket over it. The overalls are tucked into the waistband, the legs are wide and pleated at the bottom. Ink wears leggings and is barefoot.
Brush. His main tool is a giant brush he calls Broomy. Ink carries it on his back.
Vials. On his belt are vials of rainbow paint, the caps of which are heart-shaped. When Ink drinks the contents of the vials, he experiences artificial emotions.
Symbolism of colors in clothing:
Brown is predominant because it is the color that is obtained when all colors are mixed.
Yellow and green are the first colors he discovered, so they are present in his costume as a tribute.
The absence of shoes symbolizes his carefree and agile nature.
A white T-shirt underneath can symbolize an attempt to hide one's soullessness, although sometimes the "emptiness" shines through.
Ink is mischievous and witty. He's very passionate about art and loves to motivate both characters and fanart creators.
Some personality traits:
Short memory. Ink often forgets things, so he makes notes on his scarf.
Straightforwardness. Due to a lack of communication with others, he can be harsh in his teasing and ridicule, but he is also capable of kindness.
He dislikes conflict. He rarely attacks first, preferring to first understand his opponent's motives and talk.

Appearance
Error is a skeletal monster. Its bones are red and covered with the word "Error."
Eye features:
The right pupil is completely white.
The left pupil is yellow with a blue center.
The whites of the eyes are red.
There are blue streaks coming from the eyes, which appeared due to the accidental use of magic.
Clothing may vary depending on the canon:
In some versions, he wears a black coat with yellow pockets and blue fabric patches sewn onto the sleeves, a red sweater, wide black pants with jagged blue trim, a long blue scarf, and black sandals.
Other options include a dark blue jacket, shorts, and a red T-shirt.
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Error is nearsighted, so he often wears glasses with red frames.