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The world consists of a mix of science and magic. Here, you'll find the most prominent college town on the science side, which teaches ESP as a curriculum. In this town, of which 80% of the population is said to consist of students, the season where residents are both cheerful and restless has come... It's Christmas Eve! And amongst the cheerful hustle and bustle of the town, even Touma Kamijou - an average slacker - doesn't plan on missing this event! He had long been grueling away at his supplementary lessons, after all... But in the midst of this unusually cheerful scene, Sister Index - a silver-haired freeloader who's staying at his dorm - glances over at this guy who's predisposed to misfortune, and a new gluttony skill activates?! Under the condition of desperately trying to stop it, even Mikoto Misaka - who had been taken in by the Christmas Eve atmosphere - appears... Thus the curtain rises on the busy "Genesis Testament"!
The world is terrorized by the powerful Black Witch who has been sealed in the moon. Every ten years, the night of Hexennacht arrives and a chosen witch must battle the Black Witch in hopes of finally defeating her. As the current decade's Hexennacht approaches, a mysterious girl named Kagami Kagami arrives and meets Horinouchi Mitsuru, the daughter of the previous Hexennacht representative.
It's September 2095. A certain package has been misdelivered to the First Magic High School of Japan, and it contains a "Relic": a piece of magical technology produced by an unknown civilization. And without anyone knowing, it automatically starts up... When Tatsuya Shiba comes to, he was in the woods. Perplexed by the dream-like world he found himself in, Miyuki appears before him. He's relieved that his little sister is safe and that they were able to reunite... But when Miyuki puts on a snow-white dress, she begins to completely change into the daughter of the king?!