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Black Rock Shooter, known as Rock for short in the manga, is the eponymous character of the franchise. In the OVA, she merges with Mato Kuroi to help her search for her friend, Yomi Takanashi, when she is possessed by Dead Master and disappears. Her most notable physical features are her two pigtails, one long and one short, her two scars on her torso and her hip.

Source from Wikipeida