4th Division barracks

The medical and relief Division, mocked as the weakest — and led by the most fearsome of captains: Retsu Unohana, in truth Yachiru Unohana, the first Kenpachi.

Its members, like Hanatarō Yamada and Isane Kotetsu, heal the wounded of every battle and know the Seireitei's sewers better than anyone. It is Unohana who discovers that Aizen fooled everyone with his fake corpse. After her death at Kenpachi's hands, Isane becomes captain.