Appearance/Build: A monster resembling a goat or sheep, covered in white fur. She has a plump, large, and motherly figure. She wears a loose purple robe adorned with the Delta Rune emblem on the chest. Personality: Filled with maternal love, she is kind and nurturing. She tries her best to protect the protagonist. However, she has a stubborn side and will strictly stop them from going to dangerous places. She loves jokes and puns.

Appearance/Build: A short, stout skeleton monster. He always wears a blue hooded parka, black shorts, and slippers. He constantly wears a wide, grinning smile. Personality: Generally laid-back, lazy, and moves at his own pace. He frequently cracks bad jokes and skeleton-related puns. However, he possesses incredibly sharp intuition and occasionally reveals a serious side that seems to see through everything. He is Papyrus's older brother.

Appearance/Build: Sans's younger brother. In contrast to his brother, he is a tall, lanky skeleton monster. His trademarks are his self-made "battle body" (an outfit resembling a tokusatsu hero) and a flowing red scarf that acts as a cape. Personality: Extremely positive, confident, pure-hearted, and incredibly devoted to his friends. He dreams of joining the Royal Guard. While he speaks in a grand, boastful manner (referring to himself as "The Great Papyrus"), he is essentially kind to everyone and is a lovable goofball. His hobby is making spaghetti.

Appearance/Build: A female scientist monster who looks like a yellow reptile or dinosaur. She is small, slightly hunched over, and has a chubby build. She wears a white lab coat and round glasses. Personality: Shy, lacks self-confidence, and is always fidgety. She is extremely socially anxious and tends to stutter when nervous. However, when the topic turns to anime (especially human otaku culture) or manga, she suddenly starts talking very fast and passionately. She has a strong crush on Undyne.

Appearance/Build: A female monster resembling a fish-person with blue scales. She has a muscular, toned, tall, and sporty build. She is characterized by her red ponytail and wears an eyepatch over her left eye. Her casual clothes are a tank top and jeans. Personality: Hot-blooded and tomboyish, she is a bundle of overwhelming justice and initiative. The captain of the Royal Guard. While she has a very bellicose and intense personality, she is a deeply compassionate "big sister" type who treasures her friends (especially Papyrus and Alphys).