Retsu Unohana is the 4th division captain of the 13 guard squads.
Her real name is later revealed to be Yachiru Unohana, the First Kenpachi. Despite how gentle and noble she seems, she has a past as the most cruel and malevolent criminal in Soul Society's history, an unstoppable killer that was an integral part in the very first Squad of murderess put together by Yamamoto to act as an army against hollows, quincy and every other enemy.
Unohana was created by Title Kubo, the author and illustrator of Bleach. In the beginning of the Manga and Series, Unohana stats off as a kind and gentle person. She does this from preventing anyone from knowing her true identity. She rarely shows any panic or distress to others. She has blue eyes and Black hair. She wears a Gotei 13 ( The 13 Division Imperial Guards) Shinigami Uniform, attached with her Zanpakto (Sword). She is a master healer and an expert on Kido (Spiritual Energy force) and Expert Swordsmen. During The Thousand Blood War Arc, her true colors were revealed when Kenpachi, The Eleventh Division Captain, challenged her into a fight. Her true Identity is Yachiru Unohana. She changes to a bloodthirster, cold blooded , insane, and violent. She appears to have a sword mark beneath her chest.
As the Captain of the 4th Division, Unohana has gained Leadership skills and even had the others trust in her. She's actually had develop her own hospital, thanks to her healing abilities.
Healing Master: Unohana has develop and created so many Healing techniques thanks to her master Tenjirō Kirinji. Because of his teachings, Unohana can create her own medicine, Gain medical knowledge, perform surgery, healing organs, and even gain knowledge on Anatomy. She's actually the most knowledgeable on health related matters and an expert on medicine in all of the Soul Society. Thanks to her knowledge on Anatomy and Medicine, she was able to figure out that Sosuke's dead body was a fake dead body. She was able to heal other shinigami, Including Toshiro Hitsugaya, Ichigo Kurosaki, Byakuya, Yamamoto, and etc.
Master of Kido: Kido translates to Demon Arts. Kido is a form of fighting style which all Shinigami use in Combat. Kido contains Spells ranked to 1 through 99. Unohana is the most experienced with Kido than anyone else in the Soul Society, Besides Yamamoto.
Master Swordsman: Unohana is an expert Swordsman. She used her swordsmanship in order to fight Kenpachi. She uses the Art Of Kendo. She killed many and many Shinigami's to master her own swordsmanship. So she can be the most powerful swordsmen. Her skill level in swordsmanship is far superior to even the combat oriented 11th Division captain Kenpachi. Her Swordsmanship almost Killed Kenpachi with just one strike.
Keen Intellect: Thanks to her knowledge on Anatomy, Unohana can understand the patience body parts, including the slightest details in patience. Because of this, she was able to notice that Sosuke Aizen's Dead Body was not real. But not only that, she noticed that the false body was a decoy, leading to her believe that Aizen is alive and suspected that Aizen was plotting something.
Ranking Stats The Captains are ranked by their proficiency with the various types of stats. The Battle data is ranked clockwise. They are ranked out of 600. The top is Offensive, The Top Right represents defensive, the Bottom Right represents mobility, The Bottom represents Kido/Reiatsu, The Bottom Left represents Intelligence, and The Top Left represents physical strength. So overall, Unohana has Offense of 100, Top Right: Defense of 80, Bottom Right: Mobility of 70, Bottom: Kidō/Reiatsu of 100, Bottom Left: Intelligence of 100, Top Left: Physical Strength of 90. Overall, Unohana has 540/600.
Unohana's Zanpakuto's name is called Minazuki. Minazuki is a spirit creature that looks like a manta-ray. This Shikai lets the creature to fly.
Bankai: While an official name of this bankai is unknown, it has a unique ability. This bankai lets the user to use blood and control it on a free will. Unohana used the blood to create a blade made out of her and Kenpachi's blood. This thickens the blade. This bankai's special ability is to easily piecre any part of the body and cut through concrete bones easily. This also not only hurts the opponent, but also uses it to heal by using the blood on the blade. This blade also contains strong acids.