This is the "first" novella in a matched pair, the other being "The Red Threads of Fortune". While you might argue it's not necessarily fair to review just the one, only one is nominated for a Nebula.
Akeha and Mokoya are born into a world of "Slackcraft", with magical abilities based upon the traditional five elements, as a living sacrifice to seal a deal agreed by their mother, the "Protector". (Feel free to read Evil Overlord subtext into that title.)
Their world is undergoing a slow revolution, as the power of technology is overtaking that of magic, and the existing heirachies are challenged by peasants no longer held easily in their place. To throw an extra spanner in the works, Akeha is a prophet, whose visions of the future are used by their mother to attempt to cement power.
There's a lot of interesting concepts explored in the book, the most obvious of which is its gender structure. All children are born neutral, and as they age they decide which gender they are, and are then magically altered to fit. This leads to a bit of tension between our twins, when they reaslise they fall on different sides of the scale.
And the magic is quite fun, though not really built into anything resembling a rules based system.
Biggest problem with the book by miles though is the plot. It timeskips, which can be done well, but here isn't. There are too many different threads that appear out of nowhere, and fail to tie together. I've no idea why I'm meant to care about a lot of these people.
The first ten percent is fine. It sets it up nicely, gives you decent background and has some characters I'd be interested in seeing more of. Then those characters mostly vanish, and a bunch of other people run around with plotlines dangling behind them, while attempting to have a bit of development with not enough material. Don't think I'll bother picking up the next one.