When Kisaragi Ryuji's ordinary high school existence is disrupted by the reappearance of his second cousin Eriko, his life takes a thrilling turn. Together, they acquire a mysterious relic box from a shady dealer, leading them to discover the fiery dragon girl named Rose inside. To shield Rose from the clutches of a dark syndicate, Ryuji resolves to engage in combat by harnessing his abilities as a relic wielder.