I find it refreshing to see an actually clever villain for a change. Too often villains, especially in these kinds of fantasy stories, tend to be more passive. They just kind of sit around waiting for the MC to be the clever one. At most a supposedly smart villain in actuality just has plot...
That's quite a large building. If that is indeed one big magic item, then it must have taken a LOT of those magic trees to build. I wonder how many people died from Keepers and their puppets while they were harvesting all that wood?
It's almost White Walker style reproduction, but with a weirdly mutually parasitic relationship with the magic trees. Keepers use the trees to reproduce, and to make puppets, while humans use them to make magic items, and both use them as magic batteries. Only devil's eye humans can make magic...
If the only people able to make magic items are the devil's eyes, why doesn't that Owl person have one? They're supposed to be this famous magic crafter, after all.
This is why I'm always late for everything. It's not because I'm a slack-ass who waited until twenty minutes before I need to be somewhere to even start getting ready, and it takes at least a half-hour to get there.
It's because there might be monsters there, so I don't want to be first.
Like all good adventurers, even the biggest magic items only seem to exist in real space when actually in use, and they don't even need packs to carry them.