Volume 3 contains Kämpfer 11 through Chapter 15 plus one special (15.5). Natsuru begins to enroll as his Kämpfer form in the Girl Section. The reason is to leave the secret of the Kämpfer fighting remain secret from the school. Problems and complications start from the first day. Plus the possiblity of a new enemy Kämpfer and the strong rumor that he and his Kämpfer form were having a relationship which didn't sit well with Mikoto.
Soon Akane fights the new Kämpfer who didn't know that the female Natsuru is also a Kämpfer who is warned to stay clear.
With the rumor, Natsuru in his female form is confronted by Mikoto about it. Unfortunately he made it worse by accidently confirming it.
In Chapter 15, the situation with the new Kämpfer goes intense when battle erupts and ends up cause the new Kämpfer to lose the fight to Natsuru and Akane.
All it is a special not a short story with mix and match dialogues involving the characters.