Urahara Kisuke's bankai has a 'range'
...but what does that really mean?
"Kannonbiraki Benihime Aratame's power... is to restructure anything she touches."
This claim that Urahara Kisuke asserts to Askin Nakk le Vaar in Bleach chapter 666 sounds ridiculously OP, doesn't it? Where's the catch? Ah yes, it has a 'range.' I, and fandom in general, have speculated just what that limit is. We see Askin get caught in it, and his arm flayed open—only to repair itself instantly when he jumps back. So it seems that you can't get too close. We also see Kisuke's wounds reopening as Benihime collapses, so there has been much speculation (including on my part) that perhaps Benihime's restructuring expires when bankai does... the wiki seems to think so.
Well, I am here today to unveil a new (and probably controversial) opinion: That "range" has nothing to do with distance or time—it's a metaphysical one, and it hinges on the subordination of willpower.
Before I go on, I'd like to stress how fundamentally important the concept of willpower is to Bleach. This has been explored with great thought and detail by better than me, so I'll gesture to this post and this one. We saw the Hōgyoku merge with Aizen, who had a strong enough will (and hubris) to stand atop the heavens, only to see it abandon him when he began to subordinate his own will to the "will of the Hōgyoku." We know from No Breathes From Hell that with a strong enough willpower, as measured in reii, one will quite literally leave a lasting impression in the very fabric of the universe.
So: how does this apply to Kannonbiraki Benihime Aratame?
Let's take that second point first. We never, in any subsequent official material, hear about Kisuke's blindness, or even his scars. We never get any mention of how his eyes "died" again once his bankai expired and had to be restored. When we encounter him again in CFYOW, there is nary a mention about any of that. So... it seems unlikely that Cinderella's curfew applies to Benihime's restructuring.
So if there's not a duration limit to the range, what about proximity?
In a shounen manga where shinigami can't wait to shinigamisplain their bankai in great detail to their foe before using it... Urahara Kisuke breaks the pattern by playing coy. Well, of course he does; he's Kisuke, so we chuckle and think "How in character!"
But could it also be that his bankai is less effective once an opponent knows about it?
Well, of course it is. Once Askin's aware of the 'range,' he seeks to avoid it. But in the exchange that follows... see how close they are?
Kisuke's right hand is fending off Askin's while his left's being restructured. So unless we want to imagine the 'range' of proximity is tightly hugging Kisuke's body, or that he's passing on a lot of tactical opportunity here, we have to consider that perhaps proximity isn't the necessary factor.
In any case, we know the the 'range' doesn't hug Kisuke's body.
He did say "anything it touches." And we saw Kisuke laying the groundwork for that in chapter 606.
Even sealed, Benihime has still 'touched' this terrain.
But neither do we see Kisuke or Benihime physically touch Askin's left arm before he invokes bankai. (If we see that in the anime I will throw my laptop across the room and stand corrected. But it'll also be a way simpler explanation.)
In any case, he's certainly a dangerous man to touch carelessly...
Which may be why Askin's predictions turn out wrong:
Now that's a familiar-sounding overconfidence. And when we get overconfident, we can become careless.
After that initial open-arm surgery, Benihime never rearranges anything of Askin's, does she? Perhaps because he's now on guard. He's focused on keeping himself together.
And now, we circle back around to the importance of will. Here's my assertion:
Benihime can't restructure reishi that's held together by a stronger resistant willpower.
Corollary 1: if you don't want to be rearranged by Benihime, you must either concentrate on choosing not to be, or establish a pattern strong enough that it survives your loss of consciousness, or even your death.
Corollary 2: If you do want the effects of Benihime's restructuring to continue, then by all means subordinate your will to it. Especially if you're Kisuke and want to keep your new eyes. grumbles about retconning all my eye headcanons
Consider that Kisuke did nothing to rearrange the body chemistry of Yoruichi and Yuushirou as they lay unconscious nearby, suffering in Askin's Gift Bereich. I've wondered about that—but as great nobles, they have some of the highest reii of any shinigami. It's safe to say their patterns are indelible. I think that for Benihime to restructure them, they'd have to subordinate their wills, and for that, they'd have to be conscious.
What about the Gift Bereich? How is it that Benihime could make a path in, but not a path out? What's the difference?
The difference is that Askin's will established a structure that wouldn't permit creation of an exit.... even if he died. That's supremacy of willpower.
Askin's right. Why is Kisuke even asking something like this? It's almost like he's discerning just how iron-clad is Askin's intent.
Is there any support for this I can glean from Kisuke's history? Glad you asked.
We know that Kisuke has said his bankai isn't suitable for training. If it's best used on restructuring himself, that stands to reason. But we also can take something from his training of Ichigo.
"I press you a little and you fall apart!"
Advice, it has been said, is a form of nostalgia. If this is Kisuke's lesson, we can suppose it's what he learned... in his own training with Benihime. The need for resolve, for willpower, to keep from literally falling apart—could it be that's how he won his own bankai battle?