Koichi Mizuki is summoned to a world of Giant Titans by ancient magic. Arriving in the land of Tildant, the Prince, Caius, appears in front of Koichi and says, "Destiny has brought you to me. You are my fated bride!"

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Koichi agrees to stay for a month in order to get back home. However, the Prince is in a bind. He can only marry someone from another world, or else Tildant will befall a terrible fate! If Koichi doesn't stay permanently,

will the prophecy ever be fulfilled?