Meliadoul is a Shrine Knight in the service of the Glabados Church in Ivalice. She is a Divine Knight, with the ability to break an enemy's armor with her skills.
When you first encounter Meliadoul, she is your enemy. She believes Ramza to be the killer of her brother Izlude, when in truth it was Vormav in his Lucavi form, Hashamalum. Meliadoul attacks Ramza in a rage, but is unable to kill him. After being beaten, she retreats.
Later, Meliadoul goes to Limberry, and watches Marquise Elmdore turn into the Lucavi Zalera with a Zodiac Stone. Realizing Ramza had been right, she joins his party to avenge her brother and find out about her father. Nothing much more is heard about her after she joins, unless you bring her to the first fight with Vormav in Murond Holy Place (then she argues with him and basically denounces him as Izlude's real killer).
Meliadoul and Ramza make such a cute couple. They both fight for their younger sibling, and have a relative who became Lucavi. Not only that, but her status screen comment (seen above) is about love. Makes me think she's got a crush on someone, and since Ramza is the only person she's interacted with...
Hard headed and strong willed
For all the obsessors out there, her life mirrors that of Rutee from ToD (little brother dies due to a plot--although Leon comes back--possessed father, mother's identity unknown)