After the fall of the Eldeen civilization, she and her twin sister Feena came to Esteria with the black pearl With the help of the six families who were well-versed in magic, they built the kingdom of Ys. The kingdom prospered under their guidance until the series of disasters befell Ys, causing the portion of the kingdom to float. In order to put an end to the disaster, the twin goddesses sealed the black pearl with their wings and fell into a seemingly-eternal sleep until the seal gets broken 700 years later..
A slightly more than 700 years before she met Adol Christin in Esteria, her and her sister's paradise Kingdom of Ys became under attack by demons. During the war against those demons the entire kingdom was burned except of the Solomon Shrine, so together with Feena and the Six Priests she managed to use the Black Pearl's power to lift the Shrine into the sky. However, the demons started to build Darm Tower in order to gain access to the Shrine, so she and Feena went down to the burned ground of the Kingdom of Ys to investigate.
Long before that, Reah became close with the disinherited member of the Fact family, Toal Fact who served as a Holy Knight, protecting the Goddesses. She made him worry about her due to over-exhausting herself by her plan to seal all the cleria underground, but he remained her closest ally along with Feena. The night before carrying out the plan of lifting the Solomon Shrine she was visited by Toal and given the harmonica, made of cleria. It was supposed to be a goodbye as Toal secretly joined Saul Tovah in his mission to buy time for the success of the plan.
After Reah learned Toal remained behind she was saddened, but during the next six months the twin Goddesses became aware they had a traitor among them as the demons' deeds down on the surface became more and more conspicuous. The Twin Goddesses decided to leave the Solomon Shrine and descended on the destroyed surface together with the Black Pearl, claiming the ground had became even more distorted during the half-year. Later, they found Toal's broken cleria sword which saddened Reah, claiming Toal was reckless, thinking he was dead. However, his sword started to shine which meant Toal was not dead yet.
Reah and Feena entered the Darm Tower and became separated. Feena served as a bait in order to let Reah with the Black Pearl to move upstairs without any major problem. Reah eventually met Toal, now under the influence of the Demonic Essence, but this reunion was far from happy, even though she greeted him with a hope. Toal demanded the Black Pearl and then he showed her what had became of him, shifting into his demon form while retaining his sanity. Reah, with tears in her eyes, begged him to stop it as retaining both the demonic form and clear mind were very painful. Even though Toal eventually offered her to help her, she declined claiming she must do her job alone.
The two encountered each other again in the upper parts of the Darm Tower where demonic Toal almost proposed to Reah after he tried to gain more information about her plans, but she was captured by Dalles in the process. Reah was brought on top of the Tower, sealed and tortured and lost consciousness while her Black Pearl was used by her captor who used its powers to stop Toal but Dalles was defeated rather quickly. After his defeat, Dalles was finished off by Cain Fact who turned out being the traitor who manipulated the actions of all the Ys to gain more power. He merged with the Black Pearl to become Darm after Toal attempted to stop him. Nevertheless, Darm was defeated later.
Reah witnessed Toal leaving the area of battle with Darm to the top of the Darm Tower. Toal was too exhausted to stand on his own, so Feena and Reah took her harmonica back which he previously gained. She tearfully thanked him for everything he ever did for her, asked to be placed deep underground after things are done and sealed herself, Feena and Black Pearl, to become a solid statue. Obviously, she ignored Toal's demands to stop this and to try to find another way, as she and Feena did not wish to explain themselves to those who worshipped them as their Goddesses.
Toal and the rest of the successors of the Six Priests then granted them the wish and sealed the two Goddesses with the Black Pearl deep underground in the abandoned mine.
Adol first meets Reah upon his arrival at Minea. She tells Adol that she lost her silver harmonica and asks him to find it. Later on, the harmonica is found in the Abandoned Mine. Once he returns the harmonica to her, she plays her harmonica and tells Adol about the mythical kingdom of Ys.
In Darm tower, Adol meets her again at the Rado's Annex where she is held captive. Here, Reah reveals to Adol that the man responsible for her kidnapping and monsters' appearance in Esteria is none other than Dark Fact. She also tells that Dark Fact's cloak is made of the special metal called Cleria so unless Adol uses the equipment made of Cleria, Adol would have no chance of defeating Dark Fact. She gives him a monocle, which allows Adol to read the books of Ys. Lastly, she comments that although Darm tower is a scary place, she can't help but feel nostalgic for some reason...
In Ys II, Reah appears only at the end of Ys II. It is revealed that she is one of the twin goddesses of Ys along with her sister Feena. Right before the final battle against Darm, she and her sister Feena infuse Adol's cleria sword with the power of the ancient kingdom of Ys. After Adol's victory over Darm, Feena and Reah seal themselves along with the black pearl so the black pearl may not be used for evil ever again.