It's about a girl who's obsessed over a particular 'beautiful' katana that her grandfather promised her as a child. He hadn't actually think that she would request for it when she became a highschooler. On the first (or second day) she joins a sword club. The only remember realizes, when the main character takes a swing at the fake sword, that she's a natural but has a blood thirsty aura underneath. Or something like that.