Rosa became a White Mage because her mother, Joanna, was a White Mage who fought alongside her father, a dragoon, and she wishes to fight alongside her lover Cecil like her mother did with her father.

Rosa is first seen in Baron, when Cecil finds her in the castle after his mission to Mysidia and before he and Kain go on their mission to deliver a Package to the village of Mist. 

She worries for and tries to encourage Cecil, who has doubts about the King of Baron. 

She responds to Cecil's fears and doubts about his current path in life by speaking about the goodness she sees in him, that he needs to follow his heart, and lastly wishes Cecil luck on his mission to Mist before exiting his room so he may prepare for his trip to Mist.

When Cecil does not return from Mist, and after learning of the new plans of the Red Wings, Rosa becomes worried and starts searching for him. 

The specifics of her travel from Baron to Kaipo remain unknown, yet she eventually contracts Desert Fever, an illness which only the Sand Pearl can cure, and collapses on the outskirts of Kaipo. 

An elderly couple in Kaipo tends to Rosa during her malady, and when Cecil and Rydia come to visit her, they vow to find the Sand Pearl so they can cure her. 

After obtaining the Sand Pearl in the Antlion's Den with the help of Edward, they return to Kaipo and use it on Rosa, who recovers. 

Rosa then proceeds to tell Cecil about what happened after he left Baron, revealing how a man named Golbez took control of the Red Wings and actively seeks the remaining Crystals. 

Rosa then offers to assist in reaching Fabul, where its people keep the Crystal of Air -- surely Baron's next target -- as a national treasure.

Rosa, Cecil, Rydia, and Edward von Muir next cross the dangerous Mt. Hobs in order to reach Fabul. However, a thick sheet of ice blocks their path as they attempt to cross Mt. Hobs. 

Only a Fire spell can melt the ice, and only Rydia, gifted with Black Magic, can cast it, but the burning of her village has created a mental block that keeps her from casting the spell. 

Rosa helps Rydia overcome this block with encouragement and a reminder of the enormity of their quest, and Rydia overcomes her limitation and opens the way to Fabul by melting the ice. 

Further up the mountain, the party meets a man named Yang Fang Leiden, a Monk from Fabul. They help him defeat several of Golbez's monsters, and warn Yang about the impending danger to Fabul.

Upon reaching Fabul, the party provides the urgent news of Baron's intentions to Fabul's king. He accepts the help of the party, and shortly thereafter, Baron invades Fabul. 

During the battle, Rosa and Rydia take the office of relief until the invading forces push Cecil, Edward, and Yang into the Crystal Room. 

Kain's arrival in Fabul comes as a servant to Golbez, and his defeat of Cecil stops short of Cecil's death when the sight of Rosa stalls Kain's actions. 

At Kain's hesitation, Golbez enters the Crystal room and defeats the rest of the party. He taunts Cecil with the abduction of Rosa and orders Kain to take the Crystal of Air before they leave Fabul. 

Following these events, Golbez takes Rosa to the Tower of Zot and keeps her as a prisoner at its highest level. She remains bound as Golbez's captive until Cecil defeats Cagnazzo and obtains the Enterprise from Cid, at which point Kain parleys with Cecil and offers Rosa's freedom in exchange for the Crystal of Earth. 

Cecil reclaims the Crystal from the Dark Elf and fights his way to the top of the Tower of Zot, defeating the Magus Sisters to reach the top floor.

When Cecil finally arrives with the Crystal, Golbez takes it snd denies that he holds Rosa hostage. Tellah then attacks Golbez and casts Meteor on him. 

This breaks Golbez's control over Kain, and once Golbez leaves, Kain guides Cecil to Rosa in time to rescue her from certain death, barely pulling her out of the way of a trap set to fall on her from above. 

Cecil and Rosa admit feelings for each other and share a kiss, and Kain apologizes for his betrayal of Cecil and mistreatment of Rosa. 

Rosa forgives him and invites him to fight alongside her and Cecil, to which he agrees. 

The party moves to leave the tower when Barbariccia, the Archfiend of Air, appears before the party and attacks. After her defeat, Barbariccia sets the tower toward its destruction, and Rosa casts the Exit spell to warp the party from the tower to Cecil's room in Baron. 

With Golbez in possession of all four Crystals, Cecil's party worries about the next step in Golbez's plan. In response, Kain reveals the existence of the Dark Crystals, a similar set to the Crystals stolen from each prominent kingdom, these ones hidden in the Underworld. 

Kain explains that Golbez needs all eight Crystals -- the four Dark Crystals and the four already in his possession -- to open "the way to The Moon." Cecil decides that his party should head underground to protect the remaining Crystals, and Kain shows Cecil the Key of Magma. Cid's airship Enterprise had since returned to Baron via remote control.

The party then heads for the town of Agart and throws the Key of Magma in the well, opening the way to the Underworld. 

Upon descending into the Underworld, however, Cecil and his party find themselves too late. The Red Wings had already begun battling with the tanks that the Dwarves used for war. 

Damaged in the battle between the two forces, the Enterprise crash lands outside the Dwarven Castle. They enter and seek the help of King Giott, ruler of the Dwarves. 

The King, in turn, asks for their help in the fight against Golbez. While Cid takes his leave to repair the Enterprise, Yang senses something in the Crystal Room behind the throne. 

King Giott opens the way for Cecil's party to check the Crystal room. There, they find Luca's dolls, together known as the Calcabrina, under Golbez's control attempting to steal the Crystal. Cecil's party defeats them. 

Afterwards, Golbez himself appears and begins a battle with Cecil's party by summoning a Shadow Dragon that casts Hold on the entire party before its members can act. 

The Shadow Dragon eliminates each party member one by one, leaving Cecil for last. Before the Shadow Dragon can attack Cecil, the Mist Dragon appears and defeats it, leading to the sudden re-appearance of Rydia. 

Rydia offers to join the party after the battle, an offer Cecil accepts. Golbez, reduced to a single hand, steals the Crystal after this reunion and escapes.

The party next embarks for the Tower of Babil in order to retrieve the Crystals already stolen by Golbez. The party sneaks in and encounters Dr. Lugae, a scientist under Golbez working with Rubicante, the Archfiend of Fire. 

Rubicante teleports somewhere unknown, and Cecil's party disrupts and defeats Lugae. Further into the Tower, the party discovers the key to stopping the Super Cannon. When they reach it, its operators raise resistance and, upon their defeat, sabotage the Super Cannon as a last resort. 

Yang kicks the party out of the room and destroys the Super Cannon himself, and Yang is assumed dead from the explosion.

Golbez catches the party escaping from the tower and collapses the bridge while they stand on it. Luckily, Cid catches them on the Enterprise. 

The Red Wings disturb this brief reprieve by chasing the Enterprise throughout the Underground, and Cid chooses to sacrifice himself to save the party and the airship, which return to the overworld during his sacrifice. 

This act re-seals the path from the overworld to the underworld. Before Cid jumps off the Enterprise, he asks Cecil to return to Baron and talk to his workers. When Cecil does, the workers attach a hook to the airship which the party can use to pick up and carry the Hovercraft, required to reach and enter Eblan Cave.

In the cave, the party finds Rubicante fighting Edge, the Ninja prince of Eblan, the fight ending in Edge's defeat.

Edge initially refuses the party's help, yet upon witnessing Rydia's tears of mourning and the collective beauty of both Rosa and Rydia, he agrees to join citing that he doesn't like seeing Rydia, a "pretty girl," cry. 

As a womanizer, Edge's flirtatious nature finds a target primarily in Rydia, who does not care for it, yet he also shows a fleeting interest in Rosa, who responds with neither acceptance nor disdain for his attitude. 

Rosa cures the injuries Edge sustained in the fight with Rubicante, and the party enters the upper half of the Tower of Babil to find Edge's parents at the top. What begins as a warm reunion turns into a battle as Edge learns they were murdered by Rubicante and transformed into monsters by Lugae. 

They attack the party, but Edge brings them to their sense during the fight. Once Edge's parents die, Rubicante appears and apologizes for Dr. Lugae's work, followed by healing the party to full strength before their fight begins. 
The party defeats him and enters the Crystal Room, where they fall back to a lower level of the Tower of Babil deep in the Underground, discovering a new airship down the path: the Falcon.

The Falcon cannot fly over the lava, so the party heads back to the Dwarves' Castle and visits King Giott, who says that it's time to defend the last Crystal in the Sealed Cave. He gives Cecil's party the key to opening the cave: the necklace of his daughter Luca. 

In order to get the Falcon to fly over the lava, Cecil heads for the hospital to find Cid recovering. He remodels the airship for the party, so it can fly over the lava.

The party flies to the Sealed Cave, enters, and travels to the bottom where they find the Crystal. Securing the Crystal appears too easy, a sentiment that proves true when an Evil Wall tries to crush the party for removing the Crystal. 

Cecil and the rest of the party successfully overcomes this trap, only for Golbez to possess Kain again. Kain steals the Crystal and runs off, bringing Golbez the final piece Crystal he needed to complete the full set of eight. 

After Cid attaches a drill to the head of the Falcon, the party returns to the Overworld and heads for Mysidia, where the Elder's prayers finally receive an answer: the Lunar Whale, a legendary "Ship of Light from The Moon," which allows the party to fly to the Red Moon.

On The Moon, the party journeys to a palace where a man named Fusoya sleeps. Fusoya awakes and explains that Lunarian named Zemus has been controlling Golbez's actions the entire time. 

He then tells the real reason why Golbez has been gathering the Crystals. The Crystals operate as a key to activating the Giant of Babil, a giant mecha capable of decimating the inhabitants of the planet. 

The party returns to Earth with Fusoya in hopes of preventing the Giant's rise, but again find themselves too late. 

The Giant of Babil emerges from the Tower of Babil and begins its destructive spree. All hope appears lost when Cid, fully recovered, leads an army of airships and tanks controlled by leaders from all over the Overworld and Underworld, as well as friends of Cecil, to do battle with the Giant. 

Cid drops Cecil and his party into the Giant while the others distract it, and the party traverses inside the Giant. They fight the four Archfiends again on a bridge, each Archfiend taking a turn, and the party continues onward to the Giant's main computer after this victory. 

The attempt to shut down the Giant at the main computer requires the party to fight the CPU. An angry Golbez appears after the party stops the CPU, yet he does not manage an attack before Fusoya casts a spell that breaks Zemus' hold over Golbez. 

This newfound freedom of Golbez's comes with the revelation that Golbez is Cecil's brother.

At this point, the tragic history of Cecil and Golbez is revealed, finalizing in a flash back of the first meeting between Cecil and Kain during their childhood years. 

In it, Kain initiates a scuffle with Cecil over the perceived special treatment that Kain believes Cecil receives from the King of Baron, when Rosa intervenes. She reminds Kain of the moral code of men stated by the King, and when Cecil admits to starting the fight, Rosa shows admiration for Cecil's honesty.

Following these revelations, Fusoya and Golbez head to The Moon to fight Zemus, and Kain rejoins the party. 

On the Lunar Whale, Cecil asks Rosa and Rydia to leave the ship, convinced that the fight with Zemus would entail too much danger for him to allow Rosa and Rydia to accompany them for the final battle. 

The women reluctantly agree, secretly stowing away within the Lunar Whale. Once the airship lands on the moon, Rosa and Rydia reveal themselves. Rosa defends her right to join Cecil out of love and by noting her ability to cast White Magic, a skill Cecil possesses but with much less proficiency. 

Rydia, too, suggests her skills would aid in the coming battle. Cecil admits to their value and allows the women to take part in the battle against Zemus. 

They journey to the Lunar Core, where Fusoya and Golbez appear to defeat Zemus. 

However, the hatred that grew inside Zemus over the years gains its own sentience in the form of a creature called Zeromus, which continues the attack on the party. 

With help from the prayers of old friends, the party defeats Zeromus.

In the end, Cecil and Rosa marry and take the throne of Baron. All party members except Kain attend the wedding.