Summary from myAnimelist: 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.

i've gotta say this was pretty good
(tho i think most of the anime i watch is good XD......most)
but the story was good
wo girls just met and then they become close friends. but then they start to drift and one gets jealous....and the jealous one disappears

i actually dunt really know what to say about this OVA
i reallly liked it but some parts just made me think "this is abit rushed" or "they should have given Mato and Black Rock shooter more fusion time
.___. the trailers made me feel more excited like SHE'LL TRANSFORM RIGHT IN THE BEGINNING!!
the whole action trailer pump up made me abit sad cause the Ova didnt have as much Action as i thought it would have
here's the trailer

but the Slice of life stuff was really nice it made me want to be in school again (thats in a good way) and it was nice how they made it show how they became close and through those times the other universe had Death Master and Black Rock Shooter
fighting it out more brutally.

one thing i liked this anime its worth watching
but if you do listen to the Hatsune Miku Song before you watch it

it worth watching but Google the "Black Rock Shooter OVA"
and you'll find it