Akatsuki Ousawa returns to Earth after defeating the demon king Garius in the world of Alayzard, bringing back Garius's daughter Miu and passing her off as his little sister. The two enroll at Babel, a school where young people who came back from other worlds train to master the powers they picked up there, and Akatsuki runs into student council member Haruka Nanase, class representative Kuzuha Doumoto, and classmate Chikage Izumi. This manga adapts the light novel series, condensing Akatsuki and Miu's early days in a school life that keeps circling back to what he brought home.