Story about two kids who communicate with each other via magic books

Question

I read this book in English some time between 2010 and 2014.

Most of these details are vague in my memory and I may have some of them confused, but to the best of my memory these are the details:

There were two main characters, and unfortunately I don't remember either of their names. The first I remember was a girl who at the beginning of the story was searching for a flying city. If I remember right it flew by using hot air balloons. I'm pretty sure she had been born in the city and maybe even had some memories of it, and that her parents had died or gone missing, which was the reason she was looking for it. She ended up finding it and I believe went through at least one trial to become an accepted member of the society.

The second character I remember was a boy who lived in a ruined city where robot creatures had taken over and had to be avoided. I think he had a little sister. He somehow ended up in an underground fighting ring of sorts, where people would kind of merge minds with their robot creature and fight with them. His dad, who had been missing for some time, was or had been part of this, and the boy learned to do it himself and had a dog-like robot named Spot.

The girl and the boy were connected to each other and to at least two other kids through special books. The books had stories of the other kids in them, seemingly written before the stories themselves had actually taken place in the real world. The boy and girl learned to communicate either through the books or some other means near the end of the story. Also near the end, some evil creature or force became apparent, and I remember the girl either dealing with it somehow or learning about it, maybe sending a warning of some kind.

I liked the book and read it at least twice before returning it to the library, and there was a website for the authors somewhere in the cover that didn't work by the time I had the book. I know it had two authors, and I remember looking for information on a sequel and not being able to find anything at the time. I also seem to remember something about a tree, I'm not sure if it was in the title or on the cover or somehow part of the story.

I've scoured Google with various keywords, but I haven't been able to find it.

Does anyone know this book?

Answer 1

I think this is The Sky Village, first (and only) book of the Kaimira series.

From a village made of hot-air balloons to a subterranean battle arena, two young people struggle to discover who and what they are — and how to use the astonishing powers they share.

High over China, twelve-year-old Mei arrives at the Sky Village, an intricate web of hot-air balloons floating above an Earth where animals battle machines for control. Deep below the ruins of Las Vegas, thirteen-year-old Rom enters a shadowy world where he is commandeered to fight, gladiator-style, against hybrid demons for the entertainment of a mercenary crowd. Mei and Rom have never met, but they share a common journal — a book that allows them to communicate with each other and reveals that they carry the strange and frightening Kaimira gene, entwining aspects of human, beast, and machine within their very DNA. In this thrilling, intricately plotted novel, Mei and Rom must find the courage to balance the powers that lurk within — and overcome outside forces that seek to destroy them — if they are to survive and save the ones they love.

Found with a search for novel "flying city" robots boy girl books (obligatory note that Google curates search results based on what you search for and I do a lot of book searches, so that may account for me finding it)

The author's webpage was at kaimiracode.com, now gone, but you can visit the site via the Wayback Machine. As noted in the blog post linked above, the author lost control of the rights to the setting, so this is likely to be the only book.