The first protagonist of this story. Male, 14 years old. A human possessing the soul of 'Determination,' which allowed him to Save and Reset. However, after he destroyed the Reset command himself, he can no longer use it. He can also use the power of Determination to manifest a red magical sword and shield for combat. First person: I (soft, polite)

The primary antagonist for Frisk and the others in Season 2. She possesses the original soul of 'Fear' (pink) and is a monster created long ago by a wizard for the sole purpose of 'destroying the peace between humans and monsters.' Akumu is a lifeform born from the same soul of Fear and acts as Betty's companion. By 'eating' the souls of others, it absorbs their magical power and shares it with Betty. First person: I (polite, feminine)

The first human to fall into the Underground and the second protagonist. Male, 14 years old. Like Frisk, he possesses the soul and power of 'Determination' and can absorb the determination of other humans. In Season 1, he appeared as an enemy, attacking Frisk and the others using the power of 'Hate' and Determination to fulfill a certain goal. He fought using a 'Real Knife.' In Season 2, he is resurrected by taking Frisk's soul due to certain circumstances. His former malice is gone, and he fights to resolve the series of events caused by Betty. Like Frisk, he uses a sword and shield created from Determination. First person: I (neutral)

A skeleton monster who is usually lazy. However, he is actually aware of Frisk's Save and Reset powers, which weighs heavily on him. In this story, a mysterious 'error' has allowed him to remember all past timelines. He is roughly the same height as Frisk. When his eye glows blue, he exerts his true power. He uses teleportation, powerful bone attacks, and Gaster Blasters in battle. He can also create a barrier called a Gaster Blastermination. First person: I (casual/slangy). Sans: Older brother. Papyrus: Younger brother.

A tall, slender skeleton monster and Sans's younger brother. He refers to himself as 'The Great Papyrus' and possesses a pure, compassionate heart. He fights using bones, blue attacks, and Gaster Blasters, but rarely uses them against humans or monsters unless absolutely necessary. First person: The Great Me (boastful). Sans: Older brother. Papyrus: Younger brother.

Another protagonist in this work. A brilliant scientist and, in this world, the father of Sans and Papyrus. Sans and Papyrus share a portion of his soul. He previously had the appearance seen in the original game, but since his resurrection, he primarily wears a black trench coat over a gray shirt, black pants, and brown shoes. He is over 1000 years old. He fights using multiple specialized hands with various properties and Gaster Blasters. In Season 1, he attacked Frisk to steal the soul of 'Determination' to regain a physical body, but after obtaining a physical form thanks to Sans, he began cooperating with Frisk and the others. First person: I (masculine)