Fei is Shun's pet Earth Wyrm.

In her previous life, she was a girl named Mirei Shinohara (漆原 美麗), but she reincarnated as a monster instead of a human.

As a monster, her stats grow at a very fast rate, and she has excellent situational judgment. She has a cheerful, open personality, but she was a bully in her former life, and this shows in her behavior.

(Source: Official Site)