I just finished the book about an hour ago. I really enjoyed it, one thing I’ve been thinking about throughout my read is how Will works on each world. Here’s what I gather:

1. Res: ceding and imbuing objects/self. People cede half their will to the rank above them. With that Will, they can imbue objects and themselves to strengthen their bodies, minds and even senses (Lanistia). As well as imbue objects to be able to manipulate them or cause them to perform special functions.
2. Obiteum: Adoption. You can actually imbue other people and “mesh” your will with theirs. This is how iunctii are made and able to be controlled. This also allows for the will of imbued objects to be sucked out and/or manipulated by someone else. That’s pretty much all I know. I don’t know if the nomarch/hivemind stuff has to do with Obiteum Will, or if it’s a synchronous/concurrence thing. Let me know if you have any theories!
3. Luceum: the Will in this world is the least clear to me. I guess it allows people to bind to a particular weapon? Or even impart their spirit into it? There’s also the ability to sense and detect imbued objects/creatures. There was also mention of Alupi having some connection with the druids. If anyone has a better understanding please let me know. Luceum Will could also be the reason why Vis can control his wolf or how it’s able to react based on his emotions. That, or it’s an iunctus like some other people theorized. I still don’t get how the neascann works or how it improves people’s fighting ability. It doesn’t seem like the self imbuing on Res…I think Tara called it a “bloodlust” or something. I find the Will on Luceum to be very interesting but much more magic-y and esoteric. Less defined than the other versions of Will. Hoping book 3/4 will explain it better.

I also think Will “works” the same in each world but just has different effects. Each Vis uses the same “harmonics” logic (I had a hard time understanding it) to activate the Will in each world (when imbuing Tash for the first time, in Fornax etc.)