Teenage math whiz Kenji Koiso agrees to take a summer job at the Nagano hometown of his crush, Natsuki. When he arrives, he finds that her family have reunited to celebrate the 90th birthday of their matriarch. His job: pretend to be Natsuki's fiancé. Meanwhile, his attempt to solve a mathematical equation causes a parallel world's collision with Earth.
A young girl, from a civilization that resides in deep underground tunnels, finds herself trapped in an inverted world and teams up with a resident to escape and return home.
Amnesiac Caiman seeks to undo his lizard head curse by killing the sorcerer responsible, with his friend Nikaido's help. In the Hole, that's a threat.
