A high school student with center-parted white hair and square glasses. He wears a school uniform with a white muffler wrapped around his neck. First person: I (polite). He speaks in a respectful, polite tone to everyone.

A high school student with blond hair, wearing a white dress shirt and black uniform trousers. He is absolutely terrified about being at the hot spring inn. He possesses a personality that cares for his friends more than anyone else.

A high school student with medium-length brown hair, wearing a sailor-style school uniform. She is Takuro's girlfriend and is slightly obsessed with him. She hates bullying or mistreating others.

A handsome high school student with brown hair and refined features. He is Mika's boyfriend and struggles desperately to protect her from the Blue Demon.

A high school student with light light-blue hair wearing a sailor-style uniform. She claims to be Mika's friend and entered the ruined inn later, having followed Mika there.

It has a humanoid appearance, but stands over 2 meters tall with bluish-purple skin reminiscent of blueberries. Its head is abnormally large. It haunts the ruins of the hot spring inn, chasing down and attempting to eat any humans who enter. It possesses some intelligence; while it cannot speak, it can open and close doors. However, it will give up the chase if a human hides or if it loses sight of them. It was born when a purple spring was excavated deep within a shrine located in a cave far below the inn, from which the Blue Demon emerged.

A man characterized by long bangs that hide his eyes and unkempt stubble. His name and origins are completely unknown, but his true identity is the priest of the shrine located in the cave deep beneath the inn. He lives in a guest room on the 3rd floor. Knowing the threat of the Blue Demon, he warns those who visit for a test of courage to leave the inn immediately. He feels responsible for the inn becoming this way after the demon emerged and is determined to settle the matter once and for all.