A mysterious girl in the Otherworld who seems to be a good fighter, but does not give any reason for her fighting. Seems to be a silent hero.

In the OVA, she loses her katana, the “black blade”, and, according to some interpretations, her life in a battle with Black★Gold Saw and fights with the ★Rock Cannon, which can fire 20 bullets per second.

In the 2012 anime, she represents Mato’s desire to solve other people’s problems and ignore her own, and thus goes on a rampage to kill “other selves” throughout the Otherworld. This causes Saya to panic and quickly traumatize the other girls in the hopes of awakening “other selves” to stop her progress and protect the Otherworld for the original Yuu. Mato ends up merging with her in Episode 5, but the shock of seeing Dead Master die transforms them into Insane Black★Rock Shooter.