Shimazu Toyohisa is the real-life samurai who fought in the pivotal Battle of Sekigahara. In his dying moments, Shimazu is transported to a world of magic with other famous warriors throughout history. These warriors are forced to fight each other in an endless battle.
Senō Natsuru is your normal, everyday high school student. However, he's been chosen to be a Kämpfer, who's objective consists on fighting other Kämpfer with either guns, swords or magic. However, there's catch—first, you can't chose if you're a Kämpfer or not, and second, you must have the body of a girl to use your powers.
In a world where dead people turn into books and are stored in the Bantorra Library where anyone who reads a book can learn their past. Bantorra Library is maintained by Armed Librarians who wield psychic powers and their enemy is a religious society known as Sindeki Kyōdan.