Well Vanilla Kenpachi was technically one of his most powerful versions? When Unohana first encountered Kenpachi as a child he was the most powerful being she had encountered and she was the most powerful of the captains technically. He actually became weaker when he fought more people because he began to limit his own power subconsciously.
That was Kid/Teen Zaraki, and Unohana was the 1st Kenpachi. Zaraki killed the 10th, so it happened a long time after that fight.
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But his limiters increased on himself over time. He only started getting stronger again once Ichigo and he fought. And didn't Unohana fight Vanilla Kenpachi BECAUSE he killed the captain of squad 11? Or am I remembering that wrong? IIRC though, Squad 11's captain fought him first, got kill't, then Unohana stepped in the ring.
If I'm right about that, then it would make plenty of sense. Hell, that would give enough wiggle room for Squad 11's captain to be stronger than Aizen was, for christ sake. I couldn't see him being any stronger than... I dunno, Byakuya or something. I still see Unohana, Kyoraku, and Ukitake as the strongest three, before Kenpachi showed up. Excluding Yamamoto, of course.
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"Why is everybody so ****ing stupid?"- Kim Jong Il, Team America.
Anyway, yeah, the Kenpachi stuff was dumb. The only character that should have been getting weaker is Yamamoto. And Kenpachi got like... Ridiculously weaker, like he went from being Unohana level, which is presumably at least on par with Yamamoto, all the way down to scrub SS arc Ichigo level.
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"Why is everybody so ****ing stupid?"- Kim Jong Il, Team America.
He was stronger than Unohana as a child. That was just stupid. Unohana is a better swordsman than Yamamoto but he's still the stronger of the two because his Shikai/Bankai are just better in every way. Then again Unohana's healing ability is kinda stupid good so she might last a bit.
Not against 13 year old Kenpachi though. He curbs her if he feels like it.
Yeah, kinda like Goten being almost as strong as Gohan, when Goten was 7, and Gohan was 18.
But wayyyyy worse.
Question: Do we even know what Unohana's shikai and/or bankai do? We know that she summons some weird creature by using shikai, that heals people with saliva, but that's it, right? And all we know about her bankai, as far as I can recall, is that it lets her revive other people as many times as she wants to.
I really wish that we had seen Yama's full bakai though... We only got to see two of his four bankai abilities, which sucks IMO.
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"Why is everybody so ****ing stupid?"- Kim Jong Il, Team America.
Yeah. Most of them, he just kind of made to fit in with the situation.
Yachiru's is the perfect example. Her shikai is able to hit targets on all three dimensions individually, and it just so happens that her opponents ability was to vanish from one of those dimensions.
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"Why is everybody so ****ing stupid?"- Kim Jong Il, Team America.