Nightschool: The Weirn Books Collector's Edition Vol. 1 (manga)
Schools may lock up for the night, but class is in session for an entirely different set of students. In the Nightschool, vampires, werewolves, and weirns (a particular breed of witch) learn the fundamentals of everything from calculus to spell casting. Alex is a young weirn who has always been homeschooled, but when her sister, Sarah, vanishes and all memory and evidence of her existence is erased, Alex is determined to get to the bottom of it. What better place to start her investigation than the Nightschool where Sarah used to work? But when Alex discovers that sneaking into the Nightschool isn't as simple as it seems, she enrolls as a student. Is she prepared for what she might find?