Thousands of young individuals have been to fantasy realms since the discovery of "Samon Syndrome" 30 years ago, with just a handful returns retaining the exceptional powers they earned in those parallel realities. Akatsuki Ousawa, dubbed the "Rogue Hero," abandons his serene existence in the fantasy realm Alayzard in order to confront fresh difficulties when he returns to Earth. He returns with Miu, the daughter of the Demon King he vanquished, and is now compelled to conceal her actual identity by posing as his younger sister. The two are quickly accepted into Babel, an unique school for individuals who have gained exceptional talents and magical capabilities as a result of their visit to a fantasy realm. Babel appears to have been established to teach and "guide" young interdimensional explorers.