Although I lost whatever recall I had for a dream earlier… I got a coffee, sat down, and suddenly had some flash to a memory of a book, or series, that I read a long time ago. But I can’t google anything to help me find the name.
All I can remember at present, is there is a race above ground, where the protagonist comes from. They live in the trees, and can float from branch to branch with the help of some specially named cape, that attaches to their ankles (and wrists?) to catch the wind. There is also fear of another race, that lives underground, which I believe descended from the same race, which the protagonist learns somewhere in the novel(s). I believe they were called the pashaan or something similar (I remember suddenly realizing the ‘passion’ forced underground motif)
the only book i could think of with two races above and below ground is the Artemis Fowl series, and the silverwing series. It might be the silverwing series, because its about bats, and it kind of fits your descrpition, but really, I dont know