Psycome

Psycome (サイコメ, Saikome) is a light novel series by Mizuki Mizushiro with illustrations by Namanie. The first volume was published under the Famitsu Bunko imprint February 28, 2013, and the last August 30, 2014. It is complete in six volumes.

Plot
Accused of a crime he didn't commit, Kyosuke Kamiya is sent to Purgatorium Rehabilitation Academy. Suddenly, he's surrounded by a variety of fetching lasses--each one a murderer! Worse, he's famous for being the "Dozen Demon," a killer responsible for twelve deaths! When the busty, gas mask-wearing beauty Renko Hikawa approaches him, the difference between death and desire becomes very narrow indeed. How is Kyosuke gonna graduate alive?