Seikon No Qwaser

At St. Mihailov Academy, a series of serial murders have taken place with all the victims being young women. Who is this rampant culprit? And which beautiful maiden will fall prey to his evil next? After a horrible day of being harassed by their classmates, the adopted sisters Mafuyu Oribe and Tomo Yamanobe stumble across an injured young man and decide to bring him back to their place to recover. That very night, Mafuyu ends up at the mercy of the infamous serial killer. (myanimelist.net)