Okay, here's what I think will do it: Aizen's bankai will inject his illusions into every possible future, so Yhwach gets mixed up no matter what, while Ichigo cuts him down. And because Yhwach already saw everything, he already saw Aizen's bankai, so he's affected.
Alternate stupid ending: Ichigo holds out until nightfall and kills Yhwach when his powers transfer to Haschwalth.
What happens when Hashtag is dead and Yhwach needs to sleep?
Hmmm that's an interesting point. I wonder if there is a hidden level of power when a Shinigami releases their zanpakuto. Ichigo had Mugestsu, and Komamura had his human form.
If Ichigo releases his zanpakuto, Zangetsu is going to get some serious abandonment issues lol
His dad taught him the final getsuga, so presumably his dad knows how to do it. And considering this war is for all the marbles, in a sensible story he would have taught all the other good guys one by one in the hyperbolic chamber and it would be a bunch of Final whatevers.
Shame that Urahara was wasted on that other awful, awful fight.
I'm curious about Ishida.
Askin was one of the few bright spots in this arc, post-Auschwalen. The thing about Uryu is he's a schemer, and we still haven't seen the fruits of his labor yet. Also, his pops is likely several orders of magnitude more of a schemer. There are going to be traps on top of traps, and lest we forget the Ishida clan has that forbidden technique thing where they absorb all reishi, something that no other quincy to date seems to know about (back in the SS arc, Mayuri noted that it was not in any of his research notes). And Kubo might go and give Ryuken the schrift for Alpha or Omega or some other nonsense, even though Ryuuken was never part of the vandenreich. Regardless, he has right to be stupidly strong.
Hmm we'll see about that. I do want Aizen to fuck with Yhwach though.
He already did it once, you know he's gonna do it some more. Hey Yhwach, it's suddenly night time, look! Sleepy time!
I would guess the shield has a limit of like 1 normal person's HP. So Haschwald can't lose a 1v1 and if you spread it out correctly, he's beatable with 2 or more (AKA I think Ryuken is going to show up, take some damage, the shield will break, then they'll kill him).
I imagine that Isshin is going to Ichigo, though since we don't know much about his powers, I can't imagine how he'd help.
Don't forget he's gonna have a Volstandigg and he's going to be stronger than the other dude.