The Swampling King by Ben S Dobson

Long ago, the monstrous Deeplings cast the world into a vast, sunless swamp. To save their people, the disciples of the Sky God called Windwalkers raised nine cities into the sky on nine mountaintops. Ever since, highlanders and swamplings have been at war. But a time of change is near at hand…

Born to a sunless world of blood magic and monsters, Zerill dreams of leading her people into the light. But for a swampling, capture in the mountains means death.

Reluctant heir to the throne of the Nine Peaks, Prince Josen finds himself doubting the righteousness of an age-old crusade—a crusade his father would have him join.

When chance brings Zerill and Josen face-to-face, it sets in motion a series of events that will forever change both their worlds. But can they unite age-old enemies against a greater threat before it is too late for highlander and swampling alike?