Humanity, once at war with a demonic army, almost came to an end before a hero felled the leader of the monster horde, The Demon Lord. Flash forward to a time of peace, the sorcery school of Seirou Academy, built on those ancient battlegrounds, is an institute where students learn ancient magic and enter friendly competitions between countries. The newest transfer student is Lina, the clumsy grandchild of The Demon Lord, and she has her sights on Yuuya, the descendant of the legendary hero. Furthermore, she's determined to make him her bride. Problem is that once word gets out that he's the hero's decedent, a whole harem of magic users become interested in his "sacred sword"! My Bride is the Demon Lord!?