Teenager Kokoro has stopped going to school after being bullied by classmates. At home alone one day, she’s shocked to see a portal open up in her bedroom mirror. On the other side, she discovers an opulent castle. There, she meets six other lonely teenagers. The castle’s proprietor - a mysterious young girl in a wolf mask - promises one wish to whoever can find the castle’s secret key before the year is out. But she also warns of serious consequences for whoever breaks the castle’s rules…