Kris is the quiet, androgynous human protagonist of Deltarune, a teenager living in Hometown with their mother Toriel. In the Light World they have messy brown hair that shadows the upper half of their face, an olive/caramel skin tone, and wear a long-sleeved lime-green shirt with a single horizontal yellow stripe, nondescript pants, and red shoes (one lace often untied). In the Dark World their appearance shifts dramatically: their skin and hair turn cyan/navy blue, and they don silver knight-like armor (pauldrons, cuirass, gauntlets, and boots) over a navy blue bodysuit, finished with a short, torn pink-and-blue cape draped over one shoulder and heart motifs on the belt and boots. Though largely controlled by the player, they occasionally act independently—most notably by ripping out their SOUL—hinting at a complex inner life, quiet mischief, and a struggle for personal agency beneath their stoic exterior.

Toriel is a tall, white-furred goat-like Boss Monster with small horns, long floppy ears, a small tuft of fur on her head, a snout, visible fangs, and reddish-tinted eyes. In Deltarune she appears as Kris’s adoptive mother and Asriel’s biological mother, living with Kris in Hometown while working as a teacher for the younger students at the local school; she dresses casually in a lavender long-sleeve jacket, dark blouse, and polka-dot skirt, often wearing glasses and a heart pendant, and is characterized as kind, motherly, tidy, slightly old-fashioned, and fond of baking (especially pie), reading, snails, and puns.

Martlet is a blue anthropomorphic bird-like monster with two wings that double as arms. She wears a white tank top, dark blue baggy jeans and a pair of Yellow-orche snow boots. Her hair is styled as a short bob with flyaway stands and a feather-like tuft near the back. Martlet is scatterbrained, so on multiple occasions. She is forgetful, prone to rambling on during conversations, and often falls asleep at her station. She seems to struggle with concentrating on her duties. Martlet is also the mother of Berdly.