These young girls' hearts are pure, and then violent! 
Mato Kuroi just got into junior high school, and on the first day, someone catches her eye; her classmate Yomi Takanashi. The two meet. The innocent and naive Mato. The mature Yomi. Seemingly opposites, but the time they spend together only strengthens a growing friendship. But as they go into their second year at the school, they get placed in separate classes, and they begin to grow apart. 
But somewhere simultaneously... In another world, a young girl, blue fire residing in her eyes, Black Rock Shooter faces another young girl; this one holding a jet-black scythe, Dead Master, and a battle to the death begins to unfold. 
(Source: The Official Black Rock Shooter Site)

Black★Rock Shooter (OVA)