She and her twin brother were one of Raizen's before he passed away.  She is an extremely powerful fighter.  Chu also has this big crush on her, but she said she'll go out with him the day he can beat her in combat.   So far, the day hasn't come, yet.  In the Makkai tournament deciding the next ruler of Makkai after the death of Raizen, Tsume had to fight against Mukuro, and they were pretty evenly matched!

Seiyuu: I dunno... sowwy but if you do, tell me!