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.
- Guitar: Mustain can use his guitar to provide enhancement buffs to his teammates. Apparently, he is quite skilled, as he can use both offensive and defensive buffs at the same time, making him the level of a "Grand Master"
- Mustain is a tribute to thrash metal guitarist Dave Mustaine of Megadeth.