Natsuru Senou

The series' main protagonist. Second year student of Seitetsu Gakuin High-school. He is chosen as a Blue Kämpfer by Moderator and setup as a Zauber type with power based on fire. In keeping with the rule that all Kämpfers are females, he turns into girl upon transformation. After a fight with Shizuku exposed his Kämpfer form to other students of the school, Shizuku arranged to have him enrolled in girl's class to fulfil public curiosity in a way that diverts attentions away from Kämpfer battle.

His Kämpfer form has subsequently been ranked among the Three Beauties of Seitetsu (there used to be only two) and, much to Natsuru's own dismay, become subject of intense affections from Kaede Sakura (whom he has a crush on).

Source: Wikipedia