I read part I and II back to back, so I'll be putting my thoughts on both here. I already read Val's side of things previously, and I like that while both are in essentially the same predicament, it's hitting them both differently and they're facing different challenges, handling them in different ways. Comparisons aside, though, this is a really strong character piece.
I love the bond that Ignis and Amicus share, and the way that you wrote Amicus taking her pain away by literally enduring it for her. Them swapping consciousness was also a nice way to allow that while also letting Ignis work on their shared survival. The thing that really stood out, though, was the general thread of desperation through the chapters, and how it affected Ignis in a spiritual way. She begged for succor from Aquila and Castus, and they answered, providing her mending and warmth and sight. Even though it comes at a cost of her own strength, the Vis helped to keep her and Amicus alive. It's a rare thing to see, even in fantasy, and the nuance of it is something I appreciate -- it's open to interpretation and yet there's no suggestion that Ignis is somehow foolish for turning to deities in her time of need.
The relic and the Sidhe figure are quite intriguing in their own right, and there's a degree of satisfaction in seeing Ignis' experience crossing planes factoring into her story here. Combined with the promises and pleas to the Vis, it makes it seem like Ignis is there for a reason, that she's not suffering randomly. Perhaps not a 'chosen one' but chosen for the task in front of her. Or, as I've put it elsewhere, Ignis is the protagonist of her own story. I'm excited to see where this goes.