Kaze ni Mau Brigandine

Kaze ni Mau Brigandine (風に舞う鎧姫〈ブリガンディ〉, lit. "Brigandine in the Wind") is a light novel series by Takeru Koyama with illustrations by Hinata Katagiri.

Plot
I, Akechi Yoshitaka, am a healthy male high-school student. When I was invited by a senior to infiltrate the dorm of Shizuru Girls High, for some reason we ended being chased by dangerous-looking female students wielding swords. One of the girls is actually my childhood friend, Tachibana Minori. In order to save me, that girl slashed at the other pursuers! Wh-what a thing to do! Then again, the girls are all okay. But, in exchange, the skirts are taking the damage and getting torn up...!? That's right, the students of Shizuru Girls High are actually Knights clad in armor (skirts) that fight in order to take over the "Territory" inside the school!! And so it is decided that I'll be also involved in the battle aiming to become the King of Knights...!! High tension battle comedy kicking in!!