Shy outcast Kokoro has been avoiding school for weeks when she discovers a portal in her bedroom mirror. She reaches through and finds herself transported to an enchanting castle where she is joined by six other students. When a girl in a wolf mask explains that they have been invited to play a game, the teens must work together to uncover the mysterious connection that unites them. However, anyone who breaks the rules will be eaten by a wolf.
Lonely Castle in the Mirror is a Japanese novel written by Mizuki Tsujimura and published by Poplar Publishing in May 2017. A manga adaptation illustrated by Tomo Taketomi was serialized in Shueisha's seinen manga magazine Ultra Jump from June 2019 to February 2022, with its chapters collected into five tankōbon volumes. An anime film adaptation by A-1 Pictures was released on December 23, 2022.