An isolation ward dedicated to the treatment of "fairytale syndrome", best known as "Paradise".

Those afflicted with "fairytale syndrome" believe that they are characters in a fairy tale, and the inpatients here are never seen without the books of fairy tales that they treat as their bible, living their lives according to the stories written within.

Into the midst of these fairy-tale girls and their paradise comes a boy with no memory.

Who he is, why he is here or what he must do, he knows not. He cannot depend on the girls, whose devotion to their temporary roles is enviously strong.

But then he discovers a sketchbook in his room, in which is written, in a messy hand:

──One among these girls is a sinner.