I Want to Love You Till Your Dying Day 2 by Nachi Aono

An orphanage for girls is actually a boot camp, turning out magical child soldiers for a gruesome war. Yet love finds a way to blossom amid bloodshed, in this dramatic, much-anticipated yuri manga that is spiritrual kin to the likes of Revolutionary Girl Utena, Otherside Picnic,and Mobile Suit Gundam: The Witch From Mercury.

For the girls at a mysterious orphanage, death lurks behind every spontaneous giggle and childish game. With no families of their own, they are raised as magical weapons of war, taught to take the lives of others without batting an eye. Everyone, that is, except Sheena, who wishes for nothing more than the conflict around her to end. On the night of her roommate's death, Sheena meets a strange girl covered in blood, and smiling. The next day, the girl appears as a new student in Sheena's class and introduces herself as Mimi. Whispers start to drift through the halls that Mimi is a secret weapon--an immortal child soldier. Sheena's world grows even more complicated when Mimi is assigned as her new roommate. How can the peace-loving Sheena live with someone who welcomes death? And how long can she deny the effect of Mimi's strange magnetism...?