The protagonist is Kokoro, a junior high school student who has no place at school and has locked herself up at home. One day, the mirror in the room suddenly glows, and Kokoro passes through the mirror as if being sucked in, and finds a mysterious building like a castle in front of her, where seven people with similar experiences as Kokoro gather. There is a secret key hidden in the castle, and whoever finds the key can have any wish come true.