A planet where it is well known that people frequently switch between a variety of parallel universes... After his parents were divorced, Koyomi Takasaki moved home with his mother and enrolled at a nearby university prep school. Koyomi struggles to make friends because of the focus on his studies and his social ineptitude. He is one day unexpectedly contacted by Kazune Takigawa, a student, who informs him that she has come from the 85th world, where she and Koyomi are in love.