In Sheena's orphanage, girls are trained as weapons of war, except for Sheena, who longs for peace. After her roommate's death, she meets Mimi, a blood-covered girl who mysteriously joins her class the next day. Rumored to be an immortal secret weapon, Mimi becomes Sheena’s new roommate, forcing her to confront someone who embraces death while she desperately wishes to prevent it.