Five years ago, a nightmarish event on Kamioki Island left Mari Wakatake with complete memory loss while wiping out every other inhabitant of the island. Now, against her will, she is enrolled at the isolated Kaihou Academy, unaware that unseen eyes watch her, hoping her memories will return. Deep within her mind lies a chilling secret: although she survived alone, she may not have been the only survivor. As a mysterious female presence infiltrates the academy, Mari’s only chance for safety may lie with a strange girl to whom she feels an inexplicable pull, though she cannot trust her.