Umi Ryuuko (海竜虎, Ryūko Umi; lit. "sea of the dragon and tiger") was the captain of the Twelfth Division following the captaincy of Mayuri Kurotsuchi. She left her post after a failed experiment cost her shinigami powers and left her for dead in the world of the living. While living in the world of the living she had taken up a position as teacher at Domino High, teaching both Kei Noriko and Tenshi Noriko as well as running a small general store supplying Ryōga Jōkaihan with his supplies.