Aesthetica of a Rogue Hero

Akatsuki Ousawa, known as the Rogue Hero, returns to Earth after 30 years, bringing with him Miu, the daughter of the Demon King he defeated in Alayzard. To hide her true identity, Miu poses as Akatsuki's little sister, and the two enroll in Babel, a school for young interdimensional travelers. The school's stated goal is to train its students to benefit humanity and themselves, but its true purpose is unclear.