ask kenpachi and unohana
The Edge of Restraint - The Kenpachi/Unohana Relationship Being babied does not teach children how to confront problems in an effective. Unohana was the first "Kenpachi" (at the time, called Unohana Yachiru). Back in the old days, she was a bloodthirsty killer who loved. Retsu Unohana vs. Kenpachi Zaraki is a fight taking place during the Quincy Blood War between 11th Division Captain Kenpachi Zaraki and 4th Division Captain Retsu Unohana, shortly after the Wandenreich's retreat from the Seireitei. Shunsui Kyōraku reveals Unohana to be the first.
Retsu Unohana vs. Kenpachi Zaraki | Bleach Wiki | FANDOM powered by Wikia
Kenpachi refrains from discussing with Retsu the possibility of the happily-ever-after he hopes for, because she doesn't. She'll take happily-ever-after if it rolls around, but won't sacrifice quality control within the relationship to get to it. He knows that if he doesn't mention it, they don't have to fight about it, which betters his chance of getting it. Because he wants that, Kenpachi courts Retsu all over again every time they meet. This also betters his chance of getting what he wants.
Retsu Unohana vs. Kenpachi Zaraki
As part of this strategy, Kenpachi leaves tokens of his affection usually small packets of beautifully-wrapped lingerie in Retsu's quarters. He would like to leave them for her in his quarters too, but Yachiru Kusajichi knows that any wrapped package she finds there is meant for her. She didn't know what to do with the contents of a package left for Retsu, and brought the red velvet bra and panties to Ikkaku Madarame for explanation.
Kenpachi asked Retsu to shop with him for a sheath cover his blade might like, since the blade assisted him in a critical purchase of lingerie for her. She blinked at him when he proposed this, and eventually made a recommendation in jest which he took seriously. He now sports a black-suede sheath cover with a long cascading fringe. It was necessary for him to punch one but only one of his squad members for shooting him the peace sign the first time he wore it in public.
The blade likes the idea of a decorative sheath cover, but feels that the fringe is 'waaaay over the top. Knowing just how far her idiot swordsman will go to please her tickles her more.
She talks to him more frequently now that she knows he is willingly a fool for love. The zanupakuto have a relationship just as do their wielders. Both relationships include sex, but so far neither has resulted in babies, tadpoles, or a set of kitchen knives which will instantly heal you if you cut yourself while using them. When Kenpachi and Retsu are about to enter the Senkaimon, a brisk round of "You first" may take place, since each is very fond of watching the other's butt.
However, this occurs only if they are dressed in jeans, as there's not much point to ogling a shikahoushou-shrouded arse. Kenpachi allows Retsu to choose his western clothing for their forays into the Living World.
He was quite mystified by her insistence that he wear that type of western fundoshi called "briefs.
It was so sweet of you! Good times, good times. I did give my son a name! I would rather be nameless forever than be called…Foo Foo Piddlefingers. I may have been drinking.
He saw her fighting from a distance. I did wonder, when you first joined the Gotei, why you had a lieutenant with my name. I hear that a lot. This is one of my two favorite theories, currently: It would then be an Ikkaku sort of situation: I really thought you were dead. Had I known, I would have stabbed you a few more times. He used to work for her…but was kicked out.
Perhaps Kenpachi actually worked for Unohana, as part of her killing squad. But then something happened, and he was kicked out. Bleach likes exiling people, after all. And maybe Kenpachi spent all that time wandering in the Rukongai fighting to get stronger because he wanted to win his way back.
Healing is very rewarding. I would give anything to kill something again. He used to work for her…but left. Maybe he got tired of being the only guy with no name. Maybe he wanted to kill for himself and not for the system. But for whatever reason, he struck out on his own…and then later decided that he wanted to go back. Turns out you DO get more killing opportunities by being a captain than by wandering around. Unohana left Kenpachi for Squad 0.
This one is merely an addition to any of the previous possibilities in which the two of them were friends or lovers or family or coworkers. Perhaps the reason they lost touch was because Unohana was taken to Squad 0 to work for Sentoki - and by the time she came back, Kenpachi was gone.