Emerald Princess by Sofia Hammerstein

Eighteen-year-old Nicholas Hammerstein is at the cusp of finishing high school in his hometown of Los Alamos, NM. He has a seemingly ideal life and is blessed with loving parents, a cute baby sister, and great friends. Nicholas is a gifted student and martial artist who has dreams of leaving for college at the end of his senior year. But, living in a world of Emergent humans, he will soon find his life turned upside down as his life and the fate of a kingdom hang in the balance. His future and theirs will be determined by how he navigates the drastic changes in his body and the magical and superpowered Mergent population he joins.