Black Rock Shooter is a character created by HUKE. She is a pale-skinned, blue-eyed girl, with long black hair in uneven twintails - which is assumed to have been chopped or burned off during battle. She bears two stitched up scars on her belly, and wields an arm cannon and a katana. Often depicted with a single glowing eye.
Take note that the character Black Rock Shooter IS NOT Hatsune Miku, nor a Vocaloid, and shouldn't be tagged as such. However, exceptions include Hatsune Miku cosplaying as Black Rock Shooter, or when both characters appear in the same picture in a crossover.