In the land of Toyoashihara there are People of the Light and Children of the Darkness, those who worship the God of Light and his two, ruling children and those who worship the Goddess of Darkness, she who was sealed away, and the two can never meet. None of this seems to have any matter in Saya's life until a strange group of people meet her and tell her that she is one of the Children of the Darkness and she is the reincarnation of their most sacred priestess, the one who stands the best chance at over-throwing the rulers before they make the land uninhabitable for anyone. But Saya is in love with the prince of Light and these politics are both confusing and deadly, it's hard to see even what options she has much less take one that she can believe in.
This is a bit of a messy book, in the afterword Ogiwara says it was her first book which makes quite a bit of sense (she would later write the light novels for The Good Witch of the West among other things) and also says that she was heavily inspired by British children's literature which also made a lot of sense to me. It's a bit tricky to explain but there's a tendency in older British children's lit (pre-J K Rowling, ending the 70s/80s and going back decades) there the stories will sometimes introduce the plot later on so that it can instead spend extra time just moving the characters around and creating an atmosphere and tone for the story, the characters have much less control over their setting and actions in some ways. Sadly that doesn't always mean character development and that's certainly the case here, I can't really call either Saya or Chihaya (who is introduced around or slightly after the halfway point) a main character or even protagonist in this story since neither of them quite do main character-ish things. Saya remains lost and confused for much of the story, she's of the Darkness but has always grown up with the Light and yet she see's the Light doing terrible things too late for her to intervene. And when characters of the Darkness need her it's not her they need, it's her legacy as the Water Maiden, tamer of the Dragon Sword whose mere presence keeps the sword quiet. She felt like an NPC in an RPG who shows up a few times to give the players items at critical parts but that's it. Chihaya is an equally lost character with his own strange heritage which also amounts to less of what he chooses to do and more of what he already is that ends up being important. The two do grow some and end up in places where they can make choices but without a protagonist or even a main character, just two sort-of point of view characters the story itself feels a bit lost.
Some of that "lost feeling" of the story might steam from the original prose itself however, I have no doubt that the translator (Cathy Hirano) did a reasonable job since a lot of the actual word choice and structure reminded me of what I've seen in fan translations. Again, it's hard to describe, it's been quite a while since I've had a class which was this technical about English, but many of the character's actions felt oddly passive, much more so that American YA novels from roughly the same period, and I had always wondered if this was a case of a bad translation/adaptation for the fan-translations or just how these books were written. Tt seems like it's the later, there's just something odd about Japanese prose which feels stiff and stilted to someone like myself and it certainly evoke a tone for the story, although it felt more "meandering" than "mysterious" to me. I also never got the distinction between the People of the Light and Children of the Darkness, you would assume it's merely a difference in religion but people state over and over that those of the Darkness can reincarnate (and they truly can) and it seems as if being a worshipper of the Light can grant you some things too but, how does that work? Is it magic, can someone of the Light accidentally reincarnate as well? I'm probably reading too much into it but whenever you write a deep-seated conflict between two groups of people where literally everyone stands on one side or another, you have to work extra hard to make not only the conflict believable but also show why you can't be in the middle unlike nearly every real-world we see in our daily lives.
Granted, this is a series so it's possible that my complaints are addressed in later volumes and I'm simply jumping the gun. However, in that afterword Ogiwara mentions that she was writing for a new division in a publishing firm which really makes me wonder if she had a multi-book deal to start with or even plans for more books when she was writing, the ending feels a bit too neat for either of those ideas. If I had a chance to read the second book I wouldn't say no but I don't see myself seeking it out later, I'd rather try something new that I stand a better chance at liking than giving something I'm already familiar with a second shot to see if it gets better, especially since I am familiar with Good Witch of the West and I think I can spot a few quirks in all of Ogiwara's work which just don't quite work.....
I should do this more often but to recommend a similar story, this reminded me of one I read a few years ago which was called Shadows on the Moon by Zoë Marriot. It's also set in a historical, inspired-by-Japan land and stars a female main character who must navigate through a confusing situation but obviously I liked it much better. I have a review somewhere around here but it's older so readers beware of it's quality but this review on The Book Smugglers does a good job talking about it.