Between a recent move to Tokyo and the first day of high school, Rei starts his day filled with anxiety and insecurity. His nervousness accompanies him to the classroom, where amidst the classroom chatter, Rei is suddenly struck with a strange dream, followed by an aching in his chest.

Once he wakes up, Rei is greeted by a small creature standing on his desk. Passing it off as part of his dream, Rei heads home. However, to his surprise, numerous other strange creatures of all shapes and sizes roam the streets, seemingly invisible to everyone else.

With countless questions and the small creature from before trailing behind him, Rei's life is changed forever when he encounters a tall one-eyed figure, dressed in all black, smiling at him.