After winning a basketball tournament, Koichi Mizuki is magically summoned by Prince Caius Lao Bistail to Tildant, a world ruled by titans. Caius declares that Koichi is his bride and begins the bonding.

Koichi agrees to stay with Caius for a period of one month; in exchange, Caius agrees to not do anything to Koichi against his will, and to return Koichi to his home world after the month has concluded.