So, this is the choice you have made. You are just another failure. Your presence soils this Holy Tomb and disgraces my brethren. I will not allow one who would lend our enemies strength to wield the power of the goddess Sothis! I have passed judgement! And now, I shall now rip your chest open, and TAKE BACK YOUR HEART MYSELF!
~ Rhea's Breakdown upon seeing Byleth side with Edelgard.
I have no patience for foolish questions. I shall sacrifice as many lives as it takes! That apostate who insists on taking everything from me WILL BE CRUSHED BY MY OWN HANDS!
~ Rhea/Seiros to Catherine regarding Byleth.
NONSENSE! Fools who do not accept their own sins are undeserving of salvation! You humans are the ones who betrayed! You betrayed me, and you betrayed my mother!
~ The Immaculate One fighting Edelgard.

Seiros, also known as Rhea and the Immaculate One, is a major supporting character and antagonist in Fire Emblem: Three Houses, serving as the founder, patron deity and Archbishop of the Church of Seiros.

Because of her important role in the story, especially along with her own questionable motives and her descent into villainy in the Black Eagle route, Seiros can be considered as one of the two secondary antagonists (alongside the Flame Emperor) in the overall game as well.

She serves as the deuteragonist in the Acadamy Phase (as Rhea) pre-timeskip, though with questionable motives. In the War Phase post-timeskip, she serves as either an alluded character or a supporting character in most of the routes, being the deuteragonist (and the final boss after she goes berserk) in the Church route, a mentioned character in the Blue Lion route, and a major character in the Golden Deer route.

However, in the Crimson Flower route, Rhea gradually descends into madness after Byleth chooses to defy her and side with Edelgard, who was revealed to be the Flame Emperor. She becomes obsessed with killing Byleth and recovering the Crest Stone within their heart, becoming the main antagonist of the second half of the game.

She is voiced by Kikuko Inoue in the Japanese version and by Cherami Leigh in the English version.

NOTE: This page is only for Rhea/Seiros in the Black Eagle route, particularly its Crimson Flower segment, which is the only route where she serves as a villain.



According to the Church's legend, Seiros is the founder of the Church of Seiros, which named after her. It is said she received a revelation from the Goddess that was a "gift to guide the lost." However, the myth of the Church is a deliberate partial distortion of real history. Seiros was not a normal human in fact, but a member of the Nabatean race, the children of the Goddess Sothis, who lived in Zanado, the Red Canyon, before Sothis was betrayed and murdered by Nemesis, a former guardian of Seiros who became a bandit after being corrupted by Those Who Slither in the Dark. Those Who Slither in the Dark forged the Sword of the Creator from Sothis' bones, which Nemesis then used to commit genocide against the Nabateans, whose bones were also forged into weapons by Those Who Slither in the Dark.

Traumatized and embittered, Seiros became distrustful and vengeful towards humans, blaming Nemesis' hunger for power and subsequent treachery for a consequence out of human nature. She became obsessed with reviving Sothis and returning the happiness of her childhood.

War of Heroes

To exact her revenge against Nemesis, in Imperial Year 91, Seiros formed an alliance with one of Nemesis' allies, Wilhelm, by sharing her blood with him, giving him the Crest of Seiros. With the combined forces of herself, Wilhelm and the survivors of the Red Canyon, the Four Saints, Seiros led the battle against Nemesis and the Ten Elites, killing him in hand-in-hand combat at the Tailtean Plains.

After the War of Heroes, Seiros founded the Church and established the Adrestian Empire, crowning Wilhelm as its first emperor. She then proceeded to rewrite history, claiming that the Crests were gifts from the Goddess to humanity, that the Ten Elites were her devout followers, obscuring Nemesis' original past and only leaving intact that he was a hero who fell from grace. She also claimed that the weapons forged from Nabatean bones were "Heroes' Relics" gifted to humanity by the goddess, in order the hide their true nature from the people

After the establishment of the Church, Seiros began her endeavor to revive Sothis, using the Church to control Fódlan from the shadows, eliminating any who would oppose her.

Becoming Rhea

As Nabateans have a longer life span than humans, Seiros faked her death and continued to control the Church from behind the scenes. A thousand years later, she assumed the alias of Rhea and once again assumed direct control of the Church while continuing to advance her plans. As Rhea had shared her blood with Jeralt to save his life, she also used the Crest of Flames to revive a newly born Byleth, implanting its Crest Stone in his heart when he was a baby. Seiros believed that Byleth would be the perfect vessel for the Goddess.

However, Jeralt grew suspicious of Rhea due to the circumstances of his wife's death and Byleth's condition, who had a pulse but no heartbeat and never cried. Losing his faith in Rhea after believing his wife died of something else, Jeralt faked his and Byleth's deaths and left the Knights of Seiros with his child, being forced to return many years later after being discovered by Dimitri, Edelgard, Claude and Alois. In the years following Jeralt's disappearance, two of the Four Saints, Cihol and his daughter Cethleann, joined Rhea at Garreg Mach Monastary, taking the names Seteh and Flayn respectively and masquerading as brother and sister.

Black Eagle (Crimson Flower)

Note: This route can only be achieved by choosing the Black Eagle, attending Edelgard's ascension ceremony in time and choosing to spare her.

After Byleth chooses to defend Edelgard instead of killing her, Rhea grows furious with Byleth, transforming into her true form: The Immaculate One. Before she can finish them off, though, they flee. After the Adrestrian Empire and the Black Eagles successfully storm Garreg Mach Monastery, she transforms again and attacks Byelth. Byleth goes missing for five years and, unlike other routes, Rhea is not captured. In those five years, Rhea and the Church of Seiros are granted asylum within the Holy Kingdom of Faerghus by the newly crowned King Dimitri, forming an alliance with him against Edelgard and the empire and figting them to a standstill.

She slips further down into madness and revenge over Byleth's betrayal and eventually chooses to discard her alias as Rhea and just be called Seiros again. While Edelgard and the Black Eagle Strike Force capture what is left of the Leicester Alliance and either kill or exile Claude, Rhea plans an assault to recapture the Monastery in their absence, with Seteth and Flayn appearing in the battle. If fought by Byleth, Seteth notes that even he can't follow Rhea/Seiros' course anymore, despite being her advisor for so many years. They can be spared if defeated by Byleth, after which the two will go into hiding. In this scenario, Seteth will send Seiros a letter after the battle, explaining that while he despises Byleth for their betrayal, he prioritises Flayn's safety above all else. Regardless of the outcome, Seiros becomes even more furious at Byleth for taking them away from her as well.

She appears alongside Dimitri in the penultimate chapter as an optional enemy commander, hoping to intercept the Imperial army on their way to conquer Fhirdiad, the capital of Faerghus. Seiros is, of course, defeated and retreats. As the Imperial army nears Fhirdiad, she orders Catherine to torch the city, disregarding the civilians still residing there; Catherine initially objects, but reluctantly agrees. For the final battle, Seiros transforms into The Immaculate One once again and fights the Empire out of blind hatred. Upon her defeat, Byleth and Edelgard strike her down once and for all, causing Byleths' Crest of Flames to disappear and their hair and eyes to return to normal, and their heart to start beating for the first time in their life.

Other Media

Super Smash Bros. Ultimate

In Super Smash Bros. Ultimate, Seiros in her Rhea form both appears as a background character in the Garreg Mach Monastery stage and as one of Byleth's DLC spirits. As a spirit, she is an Ace level spirit under the Neutral type. In her spirit battle, the fight is set to being a stamina match on Bridge of Eldin, with the player first required to beat a Palutena, then a giant white Charizard. When equipped, she grants stronger magic attacks.



  • Seiros/Rhea is the only final boss of the game that is fought in two routes.
  • Rhea is the only major (potential) supporter of Byleth that remains unplayable in all routes, even in the Silver Snow chapter/Church route.
  • Etymology: Rhea is named after a Greek titan known as the "Mother of the Gods" due to being the mother of major Olympians including Zeus, PoseidonHades and Hera. The name may also refer to the mother of Romulus and Remus, the mythical founders of Rome.
    • Seiros may be derived from Seirios, Greek for "scorching", and an alternate name for the star Sirius.


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