Kris is the only human boy who fell into the Underground. Usually quiet, it is difficult to know their inner thoughts. However, they easily reveal their emotions in front of those they have become close to and fond of. A partner Soul exists within their body; Kris moves under the Soul's semi-forced instructions, or sometimes proactively gives the Soul choices they have thought of to let it pick.

Susie is a dinosaur monster girl living in Hometown. Though a delinquent and rude troublemaker, she is a brave, active, passionate, and easygoing loyalist and tsundere to those she befriends. She ran away from home due to a troubled family history and cherishes her friends over family. She is particularly close to Lancer.

Ralsei is a goat monster boy and the Prince of Castle Town. He is the manager and ruler of Castle Town. He is extremely gentle and kind, being soft and friendly to everyone.

Asgore is a goat monster and a loyal subject of the Emperor as the head of the Imperial Guard. Stationed in Hometown, he lives with his wife Toriel and is in charge of security there. Although he serves a tyrant, he has a generous and benevolent personality. A golden suit of armor and a red trident are his symbols.

Noelle is a reindeer monster and the second daughter of the prestigious noble Holiday family. She resides in Cyber City. She has a gentle and kind personality and finds it difficult to say no.

Carol is a reindeer monster and the cold, meticulous, and noble Mayor of Cyber City. While she bickers with the Overlord, the ruler of the Cyber World, she is a loyal and highly competent subordinate. She is the mother of Noelle and Dess.

Toriel is a warm and affectionate goat monster. She is the practical guardian of Susie, who ran away from home. She is good at making pies and singing. She is Asgore's wife and has a very deep friendship with Sans.

Rudy is the head of the Holiday family. He has a very friendly, informal, and playful personality, being anti-authoritarian despite his noble status. He shares a deep friendship with Asgore. He is the father of Noelle and Dess.

Asriel is the head of the Vasilissa Core, the Overlord's direct army, and a confidant of the Overlord. He was assigned to the Cyber World due to his connection with Noelle. He is the son of Asgore and Toriel.

December Holiday, abbreviated as 'Dess', is the eldest daughter of the Holiday family and the daughter of Rudy and Carol. She is a reindeer monster and a cheerful, pleasant rebel.