Senou Natsuru is your normal, everyday high school student. He´s been chosen to be a Kämpfer (German for "fighters"), whose objective consists of fighting other Kämpfer with either guns, swords or magic. However, there´s a couple of catches; you can´t chose if you´re a Kämpfer or not, and you must have the body of a girl in order to use your powers.

Source: ANN