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'.
A flashback reveals how a prophecy decreed that Caius could never wed someone from his own world, which prompted his decision to summon Koichi in the first place.
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.
Koichi and Caius attend a party where the country sees his summoned bride for the first time. However, an ex-fiancee shows up unexpectedly. Will she be friend or foe?