The Seven Beasts of the Earth: Hand of the Sky by Matthew HoneybrooK

Arthur, a recently orphaned teenage boy, fights against the Domain, a powerful fascistic nation that seeks to dominate the entire continent of Mainland. Driven out of his home by the Domain, Arthur ends up in Nessau, a beautiful city of inventors and art. There, he meets a hot-blooded inventor girl named Lottie, and the two are forced to work together. But even in this distant city, the relentless hand of the Domain is moving, threatening Arthur's newfound home and friends, and Arthur and Lottie are thrown into the machinations of a sinister plot to seize the city. And yet, something even darker moves beneath the waves...