Kokoro is a junior high school student, but after enduring years of bullying, she has become so anxious that she no longer attends school. One day, a girl wearing a wolf mask pulls her through her full-length mirror into a castle in another dimension. This mysterious girl informs Kokoro and six other children that they will compete in a scavenger hunt. If any of them finds a key that unlocks a secret room, that person will have one wish granted. Provided they follow the world's rules, they are free to come and go as they please. As the seven kids explore the castle, they gradually grow closer, yet the scavenger hunt remains on everyone's mind. After all, only one can win their heart's desire.