Mirai is a cat-shaped plush doll living in a mysterious castle, capable of independent movement throughout its environments. It serves as a companion to an amnesiac girl while interacting with the castle's other inhabitants. Within the group of sentient dolls, Mirai exhibits an energetic personality and leads the trio of primary doll characters. The character actively engages in dialogue, interactions, and musical sequences during the narrative. Mirai originated as a gift from Hans to his younger sister before a significant accident. During the incident, the sister held Mirai in her left arm while grasping Hans with her other arm. This event forms a foundational connection to the characters' shared history. The name "Mirai" translates to "future" in Japanese.