Hints (in case you're stuck)

First, you may or may not have noticed, but when the Ohmu travels across the screen by filling the "rage" bar completely, it destroys the golden blocks. (this became more of a main mechanic than I had anticipated, which I am aware is a bit against the spirit of Nausicaa)

You can cut vines with your staff

Some blocks can be traveled behind

I will say that there are multiple endings, and if you want the better ending (assuming you didn't already get it) I'd explore around a little more, and think of other ways to beat the boss