Fei shei are greenish tree snakes that live in warm temperate and tropical regions in and around the Xha'en Hegemony. They normally feed on small rodents, birds, eggs, and other snakes. They are also highly territorial. If approached, a fei shi drops from its perch, unfurls a pair of bat-like wings, and attacks intruders with poisonous fangs.

Fei shei possess expanding throat fans that emit a burst of bright, disorienting colors at threatening enemies. This dazzling display can incapacitate most predators and can also endanger humans who inadvertently blunder into a nest of the serpents.