This was way more focused on romance than what the summary led on (but the GR genres don't like, but I hadn't checked them, haha) and I would not say it was a good choice.
The book is full of pretty imagery once it starts explaining a bit more about Hana's world and they are all interesting places to picture in your head. There was no special focus on any place, rather we go through many due to Hana's mission. On one hand I'd have liked more depth into them, but at the same this "quick" glance was equal to all and gave a "panoramic" kind of view, so I was not fully against it. I cannot say there is truly any world-building here, but it's a world with its own rules that we don't really need to know.
What I am against though, is the depiction of Hana's and Kei's relationship. Hana wants to find her father and Kei wants to help. An interesting partnership, but the book had very specific ideas about how this partnership should work and they quickly become tiring to the reader (at least, to me). We get to see more characters coming and going and they do make this other world more solid.
The "mystery" is there, however it is not as prevalent as it should have been, while the ending just felt lackluster to me.