A young engineer hailing from the land of Ivalice, Mustadio works with father Besrodio to excavate lost technologies from the ruins of an ancient civilization buried beneath the city of Goug. Among the machines that they have uncovered is the "gun", a strange weapon capable of attacking from long distances. He meets up with Ramza along the path to Lionel Castle, and when the young Beoulve saves him and his father from the crime syndicate called the Bart Company, he agrees to join Ramza's group.

Though his guns have impressive range, they are unfortunately lacking in damage, leaving Mustadio an unimpressive dueller with a poor record. Still, he tries his best to make up for with creativity and invention what he lacks in raw power.