I was thinking about this a lot during my recent reread of Episode 8, and maybe this is a common opinion, but it all seems to make sense. Witches symbolise authors, their magic lies in their storytelling. Beatrice is a witch because of her ability to craft endless tales about the Rokkenjima incident. Eva's diary is what makes her a witch. Ikuko and Battler/Toya are witches because they're able to author the fabrications. Ange, the last Beatrice, eventually grows up to become an author. Plus, the climax happens in a library, which is pretty on the nose.

The reason you need two people to create a universe is because authors need readers. The voyager witches are critics who are capable of creating their own tales, but take greater delight in dissecting other people's. Creator witches don't need an audience, they are only writing for themselves. However, they still enjoy sharing their creations, they just don't require validation.

Without love it can't be seen. When you read a story, if you don't care for it, if you just think of it as text on a page, you aren't fully experiencing it. When you immerse yourself in a book though, you can imagine the world it is creating, you hear the character voices in your head, you become emotionally invested despite the fact that none of it physically exists.

I don't really know where else I'm going with this, I just wanted to express my feelings in public. Umineko means a lot to me, and I found this an interesting way to interpret the text as I was experiencing it again.