Lonely Castle in the Mirror [かがみの孤城]

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.