Mayuri's Bankai has already been explained. He modifies his Bankai, what's the issue in believing that? It's not the strangest feat he's pulled off by far. He could even modify his Zanpakuto so he could liquify and reassemble himself, and he even could implant dummy organs in his own body.
Saying Soifon or Gin's Bankai "breaks" is the same thing as saying Senbonzakura breaks when it splits apart. Soifon's Bankai is a missile. How stupid would it be if the missile could never regenerate? Gin also left a small, small piece inside Aizen. How do we know it even regenerates? We've only seen his Bankai once, and the missing piece was so small that you wouldn't notice it unless the panel heavily focused it. It probably does regenerate though. Because that's it's ability.....it'd be like asking why doesn't Yamamoto's Bankai turn to ashes from getting so hot. Those two Bankai have never "broken". A Bankai that involves it's very own form being changed or shedded is not the same as having it broken.
Renji's was also explained, he can just repiece his Zannpakuto together because it's connected by his reishi or whatever. It doesn't matter if it breaks. It was never ground to dust though. Don't know where your getting that, unless your talking about when Szayel canceled it. But he didn't break Renji's Bankai, he forced it to disappear because of his anti-Bankai lolscience.
Also, the idea of a Bankai not being able to be repaired easily once damaged, is very similiar to what Cirucci Thunderwitch did to her Resurrecion in her battle, where she willfully ripped off the own wings of her Resurrecion, which was not part of her ability. Almost the same concept entirely actually.
And Orihime can't heal EVERYTHING, there are some instances where her powers don't work. She couldn't heal Ichigo's Cero Oscuras wound, and like kkck mentioned above couldn't fix Tsubaki either. I don't know why, maybe because her power is still young, but it's not like this is the first time Orihime hasn't been able to fix something. Plus, she's in Hueco Mundo, and Ichigo was in SS with the RG, who are also taking his friends anyway. Which seems like the more convenient solution(well, at the time)?
1) BC Mayuri's bankai has been split in half and detonated before. We do not know the nature of this "modification," as we saw that it showed no noticeable decline in its ability against Apporo besides the change in the poison composition. If Mayuri's technology to "modify" Bankai is able to return his own to what seems to be in its original state, what's stopping Ichigo from "modifying" his own Bankai?
There is barely anything left, with even the head piece ground to dust. Mayuri's excuse that there was some of Renji's bankai that survived the attack seems almost baseless.
3) Arrancar release and Bankai release are different. Arrancar's swords are the embodiment of their hollow abilities. Zanpakuto are more of a reflection of their owners' soul that manifest into unique powers. As Thunderwitch said, detaching those arms instead of sealing them into her sword was equivalent to cutting her own limbs off.
However, Shikai can be repaired. What reason have we been given that dictates that Bankai cannot be repaired? This new, not-mentioned-before rule seems baseless and feels like the author's way of forcing the plot to explore Ichigo's shinigami power's origins.
4) Orihime couldn't repair Tsubaki bc she didn't have an understanding of how her powers worked. Thus she believed that she didn't have enough of Tsubaki to actually recover him. However, we see her resurrecting Arrancar from thin air.
As for Ichigo's cero oscuras wound, she couldn't reject, in time, Ulquiorra's reiatsu, which was preventing her from resurrecting Ichigo. There was no mention that it was impossible. More likely that she didn't have the time as Ulquiorra was right in front of her ready to finish the job.
Through Aizen, it has been established that she is capable of rejecting any event that has occurred. One limitation that has been canonized is that she is inefficient at recovering one's reiatsu. There has been no reason given as to whether and/or why she cannot repair broken Bankais.
Last edited by SuperSaiyan4; April 21, 2013 at 12:01 AM.