Mustain plays the guitar and is know by other teams to be a playboy. He was the one who found an unconscious Melrose when the Dark Air first appeared. Mustain is currently a traveling companion of Melrose, Shenandoah, Emika, and Forest Freelander.
Mustain has past-shoulder length black hair which he normally ties up. Mustain also normally wears glasses, though he takes them off when in a battle. Most of the time, he wears a long coat. When he goes to town, Mustain sometimes disguises himself in outfits ranging from just a fake mustache to a full mariachi outfit.
Mustain normally seems aloof, but during battle he can get serious as well. Also, he is known for being a playboy and often refers to himself as an "ajussi" when talking with women. He has a confident personality and a will to achieve what he wants. Mustain is a cunning man who can abandon his comrades yet caring enough to help them when they are in desperate need.
- Buffer: As a buffer, Mustain has reach the level of Grand Master for he's capable of casting both defense and offensive buff a the same time.
- Guitar: Mustain uses a guitar as his tool to buff his teammates. His specialty is to buff his team to increase their speed. He can also buff them with weapon durability which enables his team to pierce through objects that are normally impenetrable.
- Mustain is a tribute to thrash metal guitarist Dave Mustaine of Megadeth.