Rydia

Story Part I

Cecil and Kain first encounter Rydia early on in the game, during their (unwitting) mission to destroy the village of Mist - the village of which Rydia is an inhabitant. In the process, they also inadvertantly kill Rydia's mother. When the two men realize what they've done, they try to persuade Rydia to leave with them - after all, her mom is dead and her village is on fire. But Rydia wants none of that. These men just killed her mother. Being not your average defenseless child, she summons Titan. Cue havoc.

The resulting earthquake knocks Rydia unconscious, but Cecil rescues her and brings her to the village of Kaipo (Kain has disappeared at this point). While there, some soldiers from Baron arrive to kill Rydia (the king has ordered "all summoners annihilated"), but Cecil steps in and saves her life. Once Rydia sees that Cecil is not going to hurt her - quite the contrary - she relents and joins the party.

At this point, the standard Final Fantasy plotline continues for awhile. Missions, dungeons, bosses, et cetera. Rosa and Edward join the party. At one point, the group is stopped by a wall of ice when trying to get to the next village. Naturally, Rydia needs to cast fire to melt the wall, but since her village was destroyed by the fire she's never learned the spell. The encouragement of her fellow party members, who tell her that she can help save many people, finally enables her to cast the spell.

More plot. Yang joins the party, Kain steals a Crystal, Rosa gets kidnapped. The group decides to return to Baron by sea, but Leviathan appears en route and wrecks the ship. Cecil wakes up alone on a beach, and has to assume that his fellow party members are dead. At this point, the game continues for quite some time without Rydia, who may very well never reappear (but we know better). Both Edward and Yang, who were on the ship, are eventually recovered, and we learn that Rydia was swallowed by Leviathan. Not very good news.

Story Part II

Rydia, meanwhile, is quite alive and healthy, though the group doesn't know it. After Leviathan swallows her, he brings her to the Land of Summons, where she stays and learns many summon spells, black magic, and becomes friends with the summon monsters. Lucky for her! Time in the Land of Summons also passes differently, which means that Rydia ages faster while she's there.

A lot of time passes and a lot of things happen before she finally rejoins her friends. The party finds its way down to the Underworld in an attempt to protect their Crystals from Golbez (the ostensible Bad Guy). In the course of said protection, they cross swords with Golbez, who defeats them pretty easily. Enter Rydia to save the day - she appears out of nowhere, summons her trusty Mist Dragon, revives the group, and helps them defeat Golbez.

Rosa is quick to note that Rydia is now, "all grown up," and Rydia explains where she's been. She then rejoins the group, permanently this time. Rydia's story from this point on is pretty much the story of FFIV - they beat some guys up, go to the moon, beat some more guys up, beat still more guys up, kill the Zeromus, save the world. Although Rydia remains in the group from this point forward, there are few scenes that are really important to her character development.

One more noteworthy scene occurs when the party first meets up with the ninja, Edge. Although he has just been beaten in battle, he refuses to join the party because he wants to get revenge on Rubicant for killing his parents. At this point, Rydia begins to cry, lamenting the party members who have already died. It's worth noting that, although everyone in the group was saddened by the deaths of their friends, Rydia seems to be especially impacted by them. In addition, this point begins what may or may not be a harmless flirtation of Edge towards Rydia.

Story Part III

After defeating Zeromus, Rydia returns to the Land of Summons. It seems likely that since she has no other family, she will remain there. It is also evident that she keeps in touch with her friends, since she is present at Cecil and Rosa's wedding. In Edge's scene he makes a reference to "not being able to forget about Rydia" (the wording varies depending on the translation), but it isn't really known whether anything else ever happens between the two of them.