I don’t even understand these Bleach characters, lmfao. Like how do fights with them even occur.
How does a character who can see every possible future ever lose at anything? Lol
And to answer the question...
By all logic, Yhwach should be unbeatable as far as the rest of the Bleach verse is concerned, so the only way for Ichigo to beat him was through chimpanzee levels of writing.
Same with Aizen. The man just literally forgot to use his hax Shikai against Ichigo.
Keep in mind that Ichigo has no hax whatsoever. He just hits things really hard and only has a single attack technique which is just a strong sword slash.
