Bleach: Unohana's Incredible Power, Explained

gamerant.com:

This article references information from the Bleach: Thousand-Year Blood War Arc not yet released in AnimeYachiru Unohana (aka Retsu) is a gentle, dark-haired beauty responsible for health and safety as the Captain of the 4th Division in Bleach. She does not discriminate, and has been known to go out of her way to heal all those in need, be it friend or foe. Her personality exudes a distinctly non-confrontational aura and a deep sense of duty that make Unohana a very likable character, so many fans were shocked to discover that most of her Gotei 13 colleagues are actually quite terrified of this timid, tiny creature. Upon first impressions, Retsu Unohana appears to be most similar to her subordinate, Isane Kotetsu, the soft-hearted Lieutenant of the 4th Division, than anyone else. However, when delving into Unohana's history, it appears that this Shinigami medic has more in common with the brute force that is Zaraki Kenpachi, who, by all appearances, is Unohana's polar opposite. It seems unimaginable that this delicate lady would possess such bloodlust and passion for fighting, but surprisingly, in her younger days, Unohana used to be a thrill-seeking combat junkie and the Captain of the 11th Division.

Before the Gotei 13 were established in Bleach, Unohana was a criminal mastermind with sinister intent who caused mayhem and murder. However, Yamamoto saw potential in the woman and approached her with a proposition, and, along with Jūshirō Ukitake and Shunsui Kyōraku, they founded Seireitei's defense force. Unohana established the groundwork for the 11th Division, which specializes in swordsmanship, and it was only much later that she began to dabble in the healing arts, thanks to Tenjirō Kirinji's instruction. Her