Floating world

The first book in a fantasy duology from the author of The Girl Who Fell Beneath the Sea and XOXO

Suno lives in the Underworld, a land of eternal darkness. A former soldier, he doesn't remember much about his previous life. He woke up here alone with nothing but his name and his sword. Now he's just barely scraping by, until he finally stumbles upon a potential score that could change his life: a chest full of gold for whoever finds a girl who can wield silver light.
Meanwhile, far to the east, Ren, an enthusiastic acrobat, travels with her adoptive family, performing in villages large and small. But everything changes the moment a fearsome demon attacks a village during a festival. In a moment of fear and anger, silver light bursts from Ren – a power she has kept secret since childhood – and kills the monster. However, she still fails to protect her family from a devastating loss or save her beloved uncle from injury. Now, determined to prevent him from succumbing to the poison, she sets off far across the mountains from whence the monster came. The very same place Ren herself escaped from ten years ago.
Ren and Suno's paths cross, but he doesn't realise that she is the very girl he and a hundred other mercenaries are searching for. They begin to grow closer and soon discover that their pasts and destinies are far more intertwined than they could have ever imagined...