Hagure Yuusha no Estetica

In a universe where teenagers are often sucked into other worlds regularly, there is an international organization called BABEL, which trains and teaches returnees to control the magic they have brought back from different worlds. Two of their young students, returning from the world Alayzard, are brother and sister Akatsuki and Miu Ousawa. There are only some little problems here - they aren't actually related; Miu is the daughter of Alayzard’s Demon King, and Akatsuki doesn't have magic!

(Source: Manga Planet)