Retsu Unohana

is the Captain of the Fourth Division in the Gotei 13. She is one of the oldest and most experienced captains, and given her Division is of the healers, she is also a skilled healer.

History
It's hinted she has been a captain for over 200 years; along with captains Ukitake and Kyoraku. This makes her one of the eldest captains; although she doesn't appear very old.

Soul Society Arc
Unohana Retsu’s first appearance is in the emergency Captain's meeting gathered by Shigekuni Yamamoto-Genryūsai. However she says nothing at this time, and the next time she is seen is at the time of Sōsuke Aizen's death, when she confirms with Sajin Komamura and Kaname Tosen that Aizen is dead.

After that, Hanatarō Yamada is “caught” by Jūshirō Ukitake and brought before Unohana for judgment. Despite the reasons put forth by Ukitake, she determines that Hanatarō must be imprisoned on account of the fact that he is a seated officer in her division and the harm that the Ryoka has supposedly done.

As head of the medical relief division, Unohana’s healing prowess is legendary and this is shown when she next makes a major appearance, that of the time when Renji Abarai challenges Byakuya Kuchiki and is defeated by the latter’s Bankai. She manages to save Abarai from certain death, delaying her arrival at the Soukyoku Stand for Rukia Kuchiki’s execution.

Isane Kotetsu, her lieutenant, expresses the regret that Yamamoto lied to Rukia regarding the release of the ryoka, and it is at this moment that Unohana arrives and tells Isane that despite the harshness of such a lie, if it allows Rukia to leave peacefully then it is for the better good.

After the chaos of Ichigo Kurosaki arriving at the scene, destroying the Soukyoku Stand and starting his battle with Byakuya Kuchiki, the respective Captains then head off to their own battles. Unohana then releases Minazuki, even though it is not shown how, and saves all those hurt during the fighting, keeping Isane with her on top of Minazuki while allowing Minazuki to heal the rest inside of her (Minazuki). Arriving at the Relief Station, Unohana asks Minazuki to release everyone, seals Minazuki back, and asks the division members to keep the injured personnel for a time inside the station. She then asks Isane to follow her to the Central 46 Chambers.

They arrive at the scene in time to see Aizen defeating Tōshirō Hitsugaya. After that, Unohana makes her presence known by saying, “Captain Aizen. No. You no longer have the right to be called Captain. The traitorous criminal, Sōsuke Aizen.”

Aizen then replies “Domo," and asks if Unohana guessed if he was there easily.

Citing the reason that the Offices of Central 46 Chambers was the only place he could hide at and the elaborate corpse doll, Aizen then points that she made two mistakes in her analysis. The first was that he was not here to hide, and the second was immediately shown as he releases his Zanpakutō in front of Unohana and displays the “corpse doll”.

He then proceeds to tell Unohana of his Zanpakutō ability, Complete Hypnosis, and of the fact that there was a third member of the group, Tosen. He and Gin Ichimaru then teleport to Soukyoku Hill.

Unohana immediately requests Isane to find out his exact location. Upon successful location, Unohana then asks Isane to inform everyone of Aizen’s betrayal, including the ryoka, while she takes steps to save Hitsugaya and Momo Hinamori, the latter of which Aizen had fatally stabbed earlier, before Hitsugaya had made his appearance.

After ensuring that both would escape death at the moment, she leaves them in the care of Isane and travels via Minazuki to the Soukyoku Stand, where she tells Yasochika Iemura, the 3rd Seat of her division, that the ryoka do not require help (upon her observation). She then settles down beside Byakuya Kuchiki and gently scolds him, saying that he has pushed himself too hard. She then calls Rukia closer upon Byakuya’s request, and thus is Byakuya’s reason for coldness revealed.

After that, Unohana stops two 11th Squad members from creating a ruckus at the 4th Division’s Relief Station, and also tries to get Hitsugaya to talk to Hinamori, who is unconscious. He, however, gives the reply that “the way I am now, I have nothing to say to her.”

Hueco Mundo Arc
Recently, Unohana and Isane have appeared alongside captains Kenpachi Zaraki, Mayuri Kurotsuchi, and Byakuya Kuchiki in Las Noches, her appearance effectively stopping the Exequias leader from doing further harm to Yasutora Sado. He calmly orders a retreat. She stops Isane from pursuing them, claiming that they are only there to heal the injured. She proceeds to heal Yasutora Sado and Gantenbainne Mosqueda.

Personality
Unohana has a gentle and warm personality that augments her appearance. Unohana is a soft-spoken, polite, and caring woman. She uses honorifics when addressing everyone, including her subordinates, and rarely shows panic or distress. Her healing powers cannot be denied and she also has a great sense of duty, in both the times that she orders Hanatarou’s imprisonment and Isane’s chasing of Abarai when he runs away with Rukia. With her grace and kind manners, she lets others know quietly that while she may be soft, she is not to be taken lightly. Despite her gentle nature, several members of the Eleventh Division and even her fellow Captains fear her.

Also according to the former captains of the 5th and 7th squad she can be very frightening as the look on their faces implied they would never want to get on her bad side (they noted that being destroyed by Shigekuni Yamamoto-Genryūsai's Bankai would be a preferrable fate).

None has ever disputed this fact, for she is an indispensable part of Soul Society and the Gotei 13 Squads.

Powers & Abilities
Kido Master: obviously excelling in the healing branch of this form of magic.

Zanpakutō

 * In sealed form, Minazuki is slightly longer than an ordinary katana, and resembles a nodachi. Instead of tying it to her obi, Unohana carries her Zanpakutō over her shoulder by a rope strap or lets Isane carry it for her.


 * Shikai:
 * Shikai Special Ability: When unsealed, Minazuki transforms into a giant, flying, one-eyed manta-ray. It's large enough to transport many people on its back (at least a dozen, based on its size when compared to those riding it). Additionally, it can swallow even more people and transport them in its stomach, healing their injuries at the same time. When Unohana reseals Minazuki, it dissolves into green mist and reforms into the sheath of her Zanpakutō.


 * Bankai: Not Yet Revealed