Thanks to NetGalley and HarperCollins Children's Books for an advance copy!

tl;dr
A fun adventure that reads like a fable, featuring a determined young heroine.

About
Kai and Kishi are twin sisters who have done everything together. But while Kishi is the well-behaved daughter, Kai finds herself constantly pushing the limits of the rules around her. When Kishi is taken by a bakekujira (a ghostly whale spirit), Kai strikes a deal for her sister's life that will send her on an otherworldly adventure.

Thoughts
What an adventure! I've always liked reading fairy tale amalgam type books - the kind where you can see traces of Snow White and Sleeping Beauty all rolled into a new story. This is one of those books, except with Japanese fables firmly front and center. That being said, this book utterly stands on its own, and no familiarity with the original fables is necessary (many, in fact, are recapped within this very book for your reading pleasure). Kai's journey to rescue her sister combined with her personal journey of growth are interwoven very cleanly, and the story moves in a very fable-like manner from one event to the next. There are lot of big action moments, and Kai's hard work and cleverness shines through in those moments. I appreciated the focus on the bonds between family members, but also learning to accept that people sometimes grow apart, and that's not always a bad thing. A lot of Japanese terms are woven in so seamlessly that they don't break up the story at all. I was surprised that most food presented was translated, though (e.g. sliced raw fish instead of sashimi, and tofu pouches instead of inari). The ending is purposefully unclear, mimicking the dreamlike outcome of the fables it's inspired by, which might be frustrating to some readers. Hopefully it just means a sequel! Overall, a great adventure for young readers with a strong-willed lead and a lot of action.