1/5 Stars, DNF at around 250 pages. Spoilers (I guess) below. 
 Absolutely disappointing. This is the first book I have ever dropped. Others I should have dropped long ago, but it pains me to leave a book unfinished. But not as painful as trying to read this mess of a fantasy. When hearing about the plot being about two friends overcoming all odds I expected and awesome friendship like Frodo and Sam from The Lord of the Rings. Or Rand, Perrin, and Mat from The Wheel of Time. This... I'm not sure what I got. Seeing the relationship between Safiya and Iseult was short lived since they get separated around the beginning. You don't feel or experience what kind of bond they have except for the things that the characters tell you. Halfway through the book they still hardly have any sort of interaction since Iseult is sick and wounded and Safi is too busy arguing with Merik. I'm glad I stopped when I did because I'm pretty sure this book would have been more focused on a really bad romance instead of a great friendship. 
 Safi was unbearable to read. The multiple POVs helped, but obviously not in the long run. She's 18 years old in this book, but acts like a bratty, ungrateful child. Uncle Eron throws his life away to save her in an all-or-nothing plan? He's a bigger asshole than he was before. Definitely. Merik wants to sale to Nubrevna instead of stopping to get medical attention for Iseult? Let's settle this dispute by literally trying to slash his head off. This is not what a kick ass heroine looks like. She's not hot headed or short tempered. She's something else. Something that needs to be locked away. Far away. 
 Iseult was a sweetheart. A cinnamon roll too good, too pure for this book. Which makes me sad about not being able to finish this. She's a Matsi. Everyone is racist towards Matsi because... um... reasons. As many times as I flipped back through the pages I couldn't find an answer. But I really looked forward to her chapters because unlike Safi, she's not annoying in the slightest. 
 Aeduan was the only character I found any real interest in reading. It could have been because he hated every other character just as much as I did. 
 The world-building is a mess. 
 I don't even think it's right to call it world-building, since there was hardly any "building" to it. You're dropped off in an unknown fantasy world and expected to understand the surroundings of everything around you. A bunch of names and phrases you don't know the context of slapped in there to make it sound like you're reading a fantasy. Who are the Matsi, and why are they hated? What are Cleaved people? Origin Wells? This book has a map. Woohoo. You know what this book could really have benefited from? A glossary. 
 Oh yeah, this book has magic in it. There are five different types: Aether, Water, Fire, Air, and Earth. There's also an extra type called Void. Each type have many different branches of magic, and the people who use these magics are called Witches. Safi is a Truthwitch, and Iseult is a Threadwitch. Their types of witchery go in the Aether category, I think? They get their magic from... somewhere. Genetics? Tutoring? Witch-Mart? You see, it's never actually explained to you. And halfway through the book, it still hasn't been explained. Whether it was or not later on, that's way too late to be telling me that stuff. 
 This book was action-packed. WAY too action-packed. I wanted some sisterly friendship interaction and bonding, not a bunch of fighting that was very hard to follow. You can get bored through action scenes too, depending on who you are. And that's primarily why I dropped this. The lack of info about the world and the magic system didn't take me into the story. I couldn't help but feel like I was reading a book full of inside jokes that I'll never understand. The red flag was when I noticed the Emperor's sweaty hands were more intricately described than the magic system. 
 Normally I would tell someone to give a book a shot, whether I liked it or not, because they may have a different opinion of it. I can't recommend this book to anyone. I will not be reading the next installment.