Retsu Unohana is the Captain of the 4th Division in the Gotei 13. She is one of the oldest current captains and Soul Society's best healer.
Unohana wears the standard Shinigami captains uniform but instead of the normal sash it is replaces with an obi. She has long black hair that is braided down her front. She didn't have the braid over 100 years ago. Unohana carries her Zanpakuto differently to most shinigami, instead of carrying it in a sash she has a string attached to it which allows her to wear it over her shoulder. If her lieutenant, Isane Kotetsu is with her, she sometimes has her carry it for her.
Unohana is a gentle woman with a warm personality. She is a polite and caring woman who always uses honorofics when speaking to everyone, even when confronting the enemy. Even though she looks it, she uses her grace and soft manner to let others know that she is not. It is very rare she shows any sign of panic or distress either. She has a very good sense of duty which was shown when she didn't hesitate to send Isane Kotetsu to chase Renji Abarai or when she ordered Hanatarō Yamada's imprisonment. Despite her gentle nature, she has many who fear her, including several members of Kenpachi Zaraki's Eleventh Division and even other captains. According to former captains Shinji Hirako of the 5th Division and Love Aikawa of the 7th Division, she can be incredibly frightening as the look on their faces showed that they wouldn't ever like to get on her bad side.
Being the Captain of the 4th Squad, Unohana has wondrous healing abilities, and apparently is one of the most powerful Captains, despite her appearances.
Her Zanpakutō's Shikai takes the form of a giant green manta ray which has the ability to fly, and also keep injured people inside it's belly, and quickens the recovery rate of injuries.
Not much is known about Captain Unohana's past except that Captain Ukitake, Captain Kyoraku and herself, are the only remaining Captains from when the Gotei 13 was first founded.