@Tenebrous Gaze: Well, a firefly beastkin, going by how animal-like beastkin have been shown to be with Mizuko, would at most have the wings. Harder skin and constantly glowing wouldn't enter into it, though they would probably be able to light up a certain part of their body.

Um... which... corresponding with the location that lights up for actual fireflies, um... would be a bit awkward but yeah.

Basically, beastkin are humans with some animal traits appearance and ability-wise. The races that are more like anthropomorphic animals(like Golem's Ratkin) are a seperate species from beastkin.