Rereading some older Witch Hat Atelier chapters on my flight yesterday and I think some of the mystery pieces are starting to connect. Spoilers up to Chapter 87 (most recent of this writing) throughout.
We have two big lore mysteries that seem to have something to do with each other. First is the identity and intentions of Iguin, the masked witch who caused our inciting incident by giving Coco the magic book and wand:
And the other is the mystery of Quifrey's past and the fate of his other eye:
I think that the revelations of the most recent chapters gives us enough material to partially solve these mysteries.
When Quifrey was found, his eye had been taken away completely and he had been buried in a box in the ground. Planted, you might say. Now, his eye looks like this:
It's been sealed over in a way that's very similar to the way the parasitic silverwood seals over missing body parts:
(note that the person who explains the function of the parasitic silverwood to Coco is Quifrey, and he claims that he's probably the only person who understands how this works)
If it's true that Quifrey's eye has been replaced by a parasitic silverwood growing in his head, it would also explain why he feels the need to hide the truth from Olruggio - if he gets too comfortable, it will literally kill him. His goal of stopping the Brimhats is sufficiently important to him that he can't let himself be comfortable until he succeeds.
Notably, though, Quifrey isn't particularly concerned for his own sake (the implication of him not allowing himself comfort until the Brimhats are foiled is that, once he does, he knows he'll die). It's the eye he's worried about.
So it's not just that they took his eye out - they did something specific with it. I wonder what?
Let's now turn to our second mystery.
The thing that made the pieces start to connect with me, upon this reread, is this scene here:
This is the bit right after it's revealed that Iguin gave Coco some very powerful ink as a gift. The ink, it turns out, is Iguin's own blood. Metal! But we know where magic ink comes from - it comes from the silverwood tree. Indeed, Coco was able to use Custas's sap as ink in the most recent chapter:
We know that the parasitic silverwood can regrow limbs and patch over scars. And we know that its sap is ink.
So the question is: how much of a person could it regrow? How much can it replace? And most importantly, why is Quifrey on the lookout for a guy who looks just like him?
I think it's pretty clear that Iguin is a being grown from Quifrey's right eye by a parasitic silverwood tree. He wears a mask with just an eye on it because he's... literally just an eye with a body grown around it. He and Quifrey form a literal yin-yang symbol - a tree eye in a human body and a human eye in a tree body.
It makes sense for the parasitic silverwood to be such a central part of the plot of the series. It's really a perfect little bit of worldbuilding for the central theme of the series - that comfort is both the most valuable and dangerous thing in the world. Pointed-cap society has a set of rigid rules that, when applied indiscriminately, do a pretty good job of giving (most of) them a comfortable world to live in. And yet, the comfort of their rigid ideology is rotting away their society from within. They fail to see the people who are harmed by their ideology because it would be uncomfortable to do so.
We haven't seen as much of the Brimhats, so we don't really know what life is like for them, but I strongly suspect they're the opposite side of the coin. They have all the freedom and power they want, but only because they are miserable. In the most recent chapter Ininia says this basically flat out:
Their ideology is just as rigid, but it's designed to be uncomfortable, not comfortable. That's the only thing that keeps the silverwood at bay - that keeps magic from consuming them. They need to keep hating and disdaining the pointed caps because it's the only thing that keeps them going. Custas' love for his father was enough positive emotion to destroy him. How miserable must the rest be?
So, we have Quifrey and Iguin as Coco's twin teachers, each giving her one side of the coin. It's up to her to find a third way.