The people of the Sky Kingdom travel by gliders which they call solar wings. Solar wings are specialised items for soaring through the air, carried by the wind, and are fitted with a small electric motor for backup. This electric motor is charged in-flight, through the solar filament, which is woven into the wing of the glider.
Among the human Gens only the various bird Gens can effectively use this special form of transportation, since their low bone density makes them light enough to keep the gliders in the air. But this low bone density also has its obvious drawbacks: it makes the bird Gens very frail. With a body composition that allows for no extra muscles they are very prone to injury in accidents and during physical conflict.