ahhhh not mxtx related but i just finished reading the last taiki-related twelve kingdoms book and i'm so sad the fandom isn't bigger ;_;
SO. svsss people! if you're in an exploratory mood, this series is japanese but based on chinese historical aesthetics, girl/boy gets pulled to another world and it turns out they're the emperor/emperor's really important magical unicorn, respectively. (not to each other.)
i read these originally in the tokyopop translation back in the early 2000s (also when the anime was made) but seven seas is licensing a new translation, so clearly they think it'll appeal to you guys! a bunch of them are already available.
there's no romance whatsoever, a lot of it is political drama or fighting, but the characters are amazing, the ties between emperor and kirin (the unicorns) are sooo interesting, etc. (i am someone who does not enjoy reading about politics and fighting, and i still cannot put these books down. i love them.) immortal kings (gender-neutral) and their sexy, sexy assistants who can transform into flying horses. it's great.
ALSO. if you don't want to purchase. a particularly dedicated fan (RIP eugene) completed translations of all the books over a decade or more, and you can read them all here/on the site he links.
reading order: i think they're all great and would just start from #1. if you have trouble with the politics, names, etc. you can watch the anime first so that you have their faces in your mind! The OG book 1 (SS 1+2, youko + keiki) and its section of the series focus on female mcs, and the anime starts there.
but if you're coming from danmei, i can imagine that you might want to start with the male/male sets, so SS book four (enki + shoryuu, originally book 3) or the whole taiki + gyousou saga (SS book 3, OG 2). enki + shoryuu first appear in youko's story, and everything is connected but i think the different stories are designed to be able to be read standalone, so.
pithy summaries: taiki (black hair, above) is a twink who falls for (/chooses as his emperor) a hot white-haired army general. there is no way they don't have a weird codependent relationship in the later books. enki (blonde hair) similarly falls for a jaded young samurai lord and now they're both 500 years old and stuck ruling together. (one of the books is about a courtier rebelling against the emperor and i really want them to fuck.) (the emperor spends his time at brothels drinking and listening to music. he's like if shen jiu wasn't totally insane). youko (red hair) gets chosen as empress by a tall blond himbo who might be thought of as a lan wangji w/o his wwx. her best friend is a twink who turns into a rat and then she falls in with an ex-princess and a peasant. the closest this series gets to romance is youko x the rat. it's amazing.
this concludes me plugging 12k....please watch/read!!!