I won't be including a read-alikes list for this. Take a look at my first review of this book (which I've linked to at the start of my review) if you'd like some. If I were to add anything to that list, I'd probably include something from Mercedes Lackey's Heralds of Valdemar series, another epic fantasy series in which magical beings (horse-like Companions) play an important part in the kingdom's government.
Although I've previously reviewed this, I decided I'm going to write a new review for my reread.
This is my least favorite book in the series, although it was less emotionally draining to read than Sea of Shadow. The fantasy aspects of the world of the Twelve Kingdoms seemed to be less on the forefront here. Instead, the focus was on politics. It had its good moments, but the first half of the book was a slog. Also, unlike Sea of Wind, where I could see how the events of the book would fit into the more present-day history of the Twelve Kingdoms, there was very little here that seemed relevant to Yoko's time.
Book 1 was set in the present day, and Book 2 was set a few years before that. The Vast Spread of the Seas takes place 500 years before Book 1. Readers are introduced to two boys, one living in Japan and one living in the Twelve Kingdoms. Rokuta, the boy in Japan, is only four years old when he's abandoned by his parents so that the rest of his family can hopefully avoid starvation. It turns out that he's a kirin who was born in Japan, just like Taiki. He is found by his lamia and taken back to the Twelve Kingdoms. Koya, the boy in the Twelve Kingdoms, is also abandoned. He is found by a demon beast that, for some reason, chooses to take care of him rather than eat him.
In the book's present, Rokuta/Enki (I'll just call him Rokuta from here on out) is frustrated with Shoryu, his king, who seems too lazy and laid-back. This is why he doesn't make much of a fuss when Atsuyu, the self-proclaimed regent of Gen Province, has him kidnapped – he figures that maybe this will force Shoryu to finally pay more attention to his people. Unfortunately, Rokuta didn't consider that his kidnapping might lead to the thing he hates most, war and bloodshed. Occasional flashbacks show how everyone met and became the people they are in the book's present, 20 or 30 years later.
While I think those new to the series could start with either Book 1 or Book 2, I would strongly advise not starting with this book. Not only are the world rules explained in less detail, but Shoryu probably wouldn't seem worth paying much attention to. In the first half of the book, he seemed like a shoddy ruler, and his court was a mess. The advisers closest to him were excellent, but didn't trust him to do what was best for his kingdom. That included Rokuta, who believed that kingdoms would be better off without kings. Shoryu seemed remarkably unconcerned about the need for levee-building and the possible rebellion brewing in Gen Province, which only fueled his advisers' distrust in him.
I knew that Shoryu was actually a much better, sharper, and more intelligent ruler than he appeared to be, and I enjoyed the moments when he revealed this. All of his odd decisions and slacking off actually had a purpose. One thing that hit me during my reread, however, was how difficult Shoryu made things for himself by not cultivating his advisers' trust in him. I could understand why he'd want his enemies and the officials appointed by the former king to think him lazy and stupid – it meant they underestimated him. However, why not allow Shuko, Itan, and Rokuta to see more of what was really going on underneath the surface? After all, he let Ribi see that much, and as a result she was his most fiercely loyal supporter. Had Rokuta trusted him even half as much, he'd never have quietly allowed himself to be taken prisoner.
There were a lot of things I liked about this book: Shoryu's belief that rulers are nothing without their people, the deconstruction of the seemingly perfect and kind Atsuyu, Koya somehow managing to be a sympathetic character despite the things he did, and Rokuta learning to trust Shoryu more. Unfortunately, a lot of that didn't come together until the very end, so I mostly found this to be too dry and boring. I had a hard time staying interested in all the talk of levees, army sizes, and government officials.