Rydia was born in the Village of Mist, home to a rare group of people known as Callers. Callers are what the later games would refer to as Summoners, able to "Call" monsters from another land to fight for them. Rydia's mother is killed when Cecil and Kain arrive in Mist one day, unwittingly carrying a package (or ring, in the Japanese version) sent by the king of Baron, which lets loose a swarm of "Bombs" which burn the village to the ground. One thing Square says in this game which they make no allusion to in later games is that a Caller is linked intimately with the monster they're controlling, for Rydia explains, "My mom's dragon fell so my mom did too..."

   She turns on the source of her mother's death, Cecil and Kain, and accidentally drops a mountain on them by summoning a Titan. Cecil takes the unconscious girl to the inn at Kaipo, but during the night, guards from Baron arrive and tell Cecil to hand her over, because the king wants to exterminate the Callers. Cecil refuses and drives off the guards, and thus Rydia decides to trust him after all, and chooses to fight at his side. At first she has a severe fear of fire, thanks to the manner of her village's destruction, but with Rosa's help she overcomes it, and becomes able to use fire magic.

   As with Cecil, Rydia undergoes a transformation partway through the game, after she is swallowed by Leviatan, a huge monster who is the "Master of the Seas". Not only is he Master of the Seas, but also King of the Land of Summoned Monsters, from which Rydia calls her monsters. Time passes differently there, and so when she returns to save the party from Golbez, she is nearly grown up and far more powerful, though she has lost the ability to use White Magic. After returning to the Land of Summoned Monsters with the party, she asks for Queen Asura's help. The king and queen battle them to test their strength and will, and Rydia gains permission to summon them as she wishes.

   One interesting thing in Rydia's plot is that she and Edge have a sort of love/hate relationship after she returns all grown up. He flirts with her like crazy, and she scoffs at him, and yet in the Japanese version, apparently Cid accuses Edge of sleeping with her! This is complicated for a couple different reasons, one of which being that in the ending, she seems to have a little crush on Cecil (nice way to introduce a subplot... in the ending! Brilliant...), and the other is the curious problem of her age. The passing of time in the Land of Summoned Monsters is never explained exactly... so is she a child in a woman's body, or is it as if she actually lived apart from her friends for a decade?