other reading recommendations for understanding themes better?

So, I've been wanting for a while to get a deeper understanding of the manga and actually really study it, and my main obstacle is that there's a lot of relevant stuff that I'm not particularly knowledgeable on (mainly regarding Buddhism, Japanese culture, mineralogy... a bit of everything, really.) I'm wondering if people have some nonfiction book recommendations? I'll accept video format stuff too if it's really good but I find written media considerably easier to get into.