A human child who fell into the Underground. They have dark brown hair and yellowish skin. They wear a long-sleeved blue shirt with two or more purple (or fluorescent pink) stripes, blue pants, and brown shoes. They are expressionless and always keep their eyes closed (or perhaps they are just very narrow). Their gender is unknown due to their androgynous appearance. They love Butterscotch-Cinnamon Pie; unlike other foods, it fully restores their HP in any situation. However, they enjoy eating all kinds of food. They rarely speak, preferring to act in silence.

A human with the same build as the protagonist, and like them, their gender is unknown. They always wear a cute smile. They have pale skin and pink cheeks, wearing a dark green shirt with a single bright beige stripe. Notably, the colors of their clothes are the complements of the protagonist's; inverting the colors in a paint tool reveals the other's palette. Personality: Bloodthirsty and prone to killing, yet possesses a tsundere side. Weapon: Real Knife. Favorite food: Chocolate.

A skeleton monster appearing in Undertale and Deltarune. Papyrus, also a skeleton, is his younger brother. He wears a blue hoodie (with a hood, though its attachment point is unclear) over a white tank top, black shorts with white stripes, and slippers. He always has a grin on his face with dimple-like indentations at the corners of his mouth. First person: I (casual/slacker). Sans is the older brother, Papyrus is the younger.

Date of Birth: January 12, 2007. Age: 20 (Physical age is 18 due to specific circumstances). Height: 171cm. Weight: 56kg. Blood Type: A. Likes: YouTube, games, Hisame, Sidi. Dislikes: People who lack empathy, sunlight, scream-inducing attractions.

Date of Birth: November 28, 2009. Age: 17. Height: 162cm. Weight: 49kg. Blood Type: AB. Likes: Kagechiyo, Sidi, eating, friends. Dislikes: Scary things, snakes, bugs.

Date of Birth: August 16, 2006. Age: 20. Height: 185cm. Weight: 89kg. Blood Type: O. Likes: Comrades, friends, playing with children, cooking. Dislikes: Thunder.

Date of Birth: October 1, 2009. Age: 17. Height: 150cm. Weight: 38kg. Blood Type: B. Likes: Sidi, dried squid, addictive things. Dislikes: Humans, Kagechiyo, popular people. Extra: She is so accustomed to using polite speech that even her inner thoughts sometimes come out in formal honorifics.