Yuki Tachibana, a withdrawn first grader, is convinced that the fourth floor of his school is home to supernatural creatures that few kids (and no adults) can see and he's worried about a recent influx of new, less friendly creatures and about his ability to perceive the true shape of things waning as he gets older. Most of the other kids mock Yuki, who they think is crazy due to his strange pronouncements and peculiar actions, and, aside from the creatures he sees, his only social interactions are with the school's kindly and open-minded caretaker, a new transfer student named Makoto Suzuki who's allocated the desk next to his and an enigmatic boy named IQ who always wears a box over his head.