Aria the Scarlet Ammo

Second part of the Hidan no Aria manga adaptation, adapting volumes 7 through 9.

Tokyo Butei High school--- It was a special school where armed detectives, also known as "Butei" are being brought up. Tohyama Kinji is a sophomore student who has the unique body which activates a "super mode" when it was stimulated by "something". He tries to hide it to others in order to live a peaceful life. But trouble came to find him when he became a victim of a bombing incident, where he met the Butei high "Assault" department elite, Aria H. Kanzaki. (Source: Baka-Tsuki)

The girls of Hidan no Aria star in their own super-deformed 4-koma comic series, most of which fall under girls doing cute things. Not nearly as many guns as you'd expect there to be.