Seteyn

Seteyn is the family ship between Seteth and Flayn from the Fire Emblem fandom.

Fire Emblem: Three Houses
In the ancient past of Fódlan, the Nabatean Cichol fell in love with a woman and the two had a child - a daughter named Cethleann. Years later, Cichol and Cethleann would join another Nabatean, Seiros, in the conflict that would become known as the War of Heroes - an act that would lead the two of them to become recognized as Saints. During the conflict, Cethleann would be gravely injured to the point of going into a coma for centuries, forcing Cichol - who also lost his wife/Cethleann's mother in the conflict - to go into hiding so she can recover. Cethleann would finally awaken in Imperial Year 1179, by which point Cichol had reconnected with Seiros - who now goes by Rhea - and now acts as her second-in-command under the new name of Seteth. She would join her father at Garreg Mach Monastery under the name Flayn, and the two also decided to act like siblings to further hide their true identities.

Part I: White Clouds
The year after Flayn's awakening, she and Seteth become acquainted with Byleth Eisner, a mercenary that Rhea has brought on to teach at the Monastery's Officer's Academy. Seteth would go on to assign Byleth and their class monthly missions for the Church of Seiros while Flayn would spend her time fishing while occasionally helping her father such as during the annual Goddess's Rite of Rebirth ceremony. During that particular ceremony, Flayn tells Byleth's class that Seteth said they'd be better off patrolling a coffin, which he doesn't take too kindly to her revealing. Despite Seteth saying it was a joke, the suggestion leads Byleth's class to stop an attack on the Holy Mausoleum. A month after the Rite of Rebirth, Flayn suddenly goes missing. In a panic, Seteth searches the entire monastery for her before asking Rhea and Byleth if they've seen her - only to be met with no's. After some investigation, Rhea determines Flayn hasn't left Garreg Mach and tasks Byleth's class with finding her as the monthly mission. In the meantime, Seteth organizes the Knights of Seiros to sweep nearby towns for information - all while still fearful about Flayn's safety given rumors of a "Death Knight" cropping up lately. Eventually, Byleth's class manages to find Flayn - who'd been captured by the Death Knight and held in Garreg Mach's catacombs - and bring her back to safety. Seteth is grateful to Byleth for rescuing her - but after realizing the kidnapper (who was also part of the attack during the Rite of Rebirth) was likely after the secret within Flayn's blood, Seteth decides the two of them should go into hiding. Flayn, however, rejects the idea as there's no guarantee their hiding spot would work and she doesn't want to be alone again. Instead, she suggests joining Byleth's class so they can protect her - a plan that Seteth begrudgingly admits has merit. With that, Seteth entrusts Flayn's safety with Byleth. Sometime after the mission in Remire Village, a group of soldiers from the Western Church attack Rhodos Coast and begin taking the artifacts held at the monument to Saint Cichol. Seteth makes preparations to help drive them off, but Flayn desperately insists on coming along - which Seteth vehemently denies as he doesn't need the stress of worrying about her safety. The argument is interrupted when Byleth arrives to figure out what's happening, prompting the two to explain it. After the explanation, Flayn realizes that having Byleth's class come with them would alleviate Seteth's worries about her safety - which he admits would be correct. With the backing of Byleth's class, Flayn and Seteth manage to drive off the Western Church forces from the coast. Following the battle, Seteth tells Byleth that the monument is also where his wife was buried - just as they overhear Flayn honoring her mother's grave. When Byleth asks about that coincidence, Seteth and Flayn decide to come clean and reveal their true nature as father and daughter to them. Seteth explains why he and Flayn have to pose as siblings (although leave out that they're Saints Cichol and Cethlenn) and has Byleth promise to never reveal the truth to anyone. The father and daughter soon begin reminiscing about their late wife/mother, and their time at Rhodos Coast, before agreeing to live their lives to the fullest for her. Things go south when one of the leaders of Garreg Mach's houses - Edelgard - declares war on the Church of Seiros by launching an attack on the Holy Tomb. In the aftermath, Flayn overhears Seteth talking with Rhea about what to do next. After Seteth agrees to watch over Byleth - who Rhea reveals is the vessel of the creator goddess Sothis - Flayn comes out of hiding and proclaims that she'll help out with that. Seteth is slightly annoyed she was eavesdropping, but is thankful that she's so willing to help Byleth since they're the reason she's still alive. Soon, however, Edelgard - now Emperor of the Adrestian Empire - raises an army and moves in to claim Garreg Mach for the Empire. Seteth and Flayn join Byleth's class in attempting to fight off the invading army, but the battle goes poorly thanks to the disappearance of both Byleth and Rhea. With that, Garreg Mach is left to ruin as Seteth, accompanied by Flayn, rally the Knights of Seiros in the hope of finding Rhea.

Part II: Silver Snow
Five years following the Battle of Garreg Mach, Seteth miraculously finds Byleth in the ruins of the Monastery and - after helping them clear some bandits - brings them to Flayn, who was in the Holy Mausoleum for something. The two are overjoyed to be reunited with Byleth and find new hope in locating Rhea. With the gathering of the Knights of Seiros and Byleth's former class, and having decided Garreg Mach to be their base of operations, Flayn agrees to let Seteth handle getting new allies to fight the Empire while Byleth and the rest focuses on restoring the monastery. Later that month, the two join Byleth in presenting the new flag the Knights will fight under - emblazoned with Byleth's Crest of Flames. Following the ceremony, Flayn privately inquires to Seteth and Byleth about why Edelgard launched her war to begin with. This prompts a discussion between the three that ends with Seteth believing that Edelgard wants to rebuild Fódlan by tearing down its old institutions. When Flayn points out Edelgard's plan will only cause hurt among Fódlan's people, Seteth agrees and vows that they must stop her to save the nation - which Flayn is thankful for. As Flayn begins inquiring about where Byleth was for the past five years, the Empire launches another attack on the Monastery that she and Seteth join in repelling. Seteth and Flayn continued assisting Byleth in their fight against the Empire until finally managing to kill Edelgard in the Adrestian capital of Enbarr, which is also where Rhea was being held captive. Following the battle, Flayn is handed a letter from a surviving Imperial soldier and gives it to Byleth, who Seteth was talking with. The three read the letter - written by Edelgard's retainer Hubert - and learn that Adrestia was working with a mysterious group before revealing the location of both their safe have and where Rhea is. After reading the letter, Seteth and Flayn realizes that the group, "Those who slither in the dark", are enemies of the "children of the goddess" - Nabateans like them - and are the same ones that orchestrated Flayn's kidnapping years ago. Finding Rhea, they learn that they're also the same group that helped the King of Liberation Nemesis in the ancient past. After realizing that they were using Edelgard as pawns for their plan, Flayn proposes going to them and stopping them. With both Seteth and Flayn advising preparedness, Byleth and their army head for "Those who slither's" hideout of Shambala. There, the two Nabateans help in defeating the leader Thales and finally ending their threat for good. The army manages to escape just before Thales manages to level Shambala, at the cost of Rhea - who joined the battle - being severely wounded. Back at Garreg Mach, Seteth and Flayn join Byleth in watching over Rhea as she recovers. During that time, they finally reveal to Byleth that they, and Rhea (although Byleth suspected already), were "children of the goddess" before asking them to consider leading Fódlan in the event that Rhea doesn't survive. At month's end, at Garreg Mach's outer wall, the four gather to hear Byleth's answer - only to be interrupted when Rhea's draconic blood starts driving her insane as she turns into the Immaculate One and flies off. After hearing other priests and knights were also transforming, Seteth realizes that Fódlan is doomed unless Rhea is killed. Reaching the maddened Rhea, Seteth and Flayn mournfully help Byleth and their army in subduing her but manage to do so without killing. With that, peace finally comes to a now-unified Fódlan.

Support Conversations and Paired Ending
Sometime after Flayn's kidnapping, Seteth looks for and eventually finds her. Seteth is thankful to have found her after having worried about her time with the Death Knight, but Flayn believes he's worrying too much - especially since the kidnapping opened the way for her to be in Byleth's class. Seteth, however, is not happy about that view before coming to the reason he sought her out: asking her about if any other students had tried something with her. Flayn assures him that the other students have been treating her well, but starts getting annoyed when he keeps pressing her about any potential trouble. She finally snaps and tells Seteth that there is someone getting in the way of her making friends - before revealing it's him before leaving. Now alone, Seteth tries to rationalize what Flayn was getting at but fails and vows to himself to keep her safe. After their discussion, Seteth goes around asking people about what they think of Flayn. She becomes aware of this and confronts him about butting into her relationships again. Despite Seteth claiming all the people say they get along with her, Flayn expresses how embarrassed she was about the trouble he caused, even specifically mentioning a person Seteth talked to in the dining hall that now feared for his life. Realizing who she's talking about, Seteth notes the person had obvious feelings for Flayn and he wanted to test his resolve by asking if he would risk his life for Flayn. However, Flayn assets they were friends and nothing more before demanding Seteth to stop meddling with her relationships since she's not a child. Seteth notes that she does trust her, but he feels responibilities by being her elder brother - which Flayn brushes off before leaving him alone. Sometime after Byleth's five-year disappearance, Seteth approaches Flayn with the latter already assuming he's there to pester her as she's come to accept that nothing will make him less protective of her. When Seteth admits that he is overprotective, Flayn apologizes for it since she's the source of it - only for Seteth to turn it around and apologize for not being able to save her or her mother during the War of Heroes. At that, Flayn admits to Seteth her fear of falling asleep only to never wake up, before noting her fear of being alone is greater and she just wants to be treated normal just as her mother was treated around Seteth. When Seteth admits that Flayn is right, she goes on to temporarily drop their facade as brother and sister for that moment to express her gratitude for their quiet times together and her desire to grow. Seteth, in turn, accepts her desire but asks that, as her father, he continue protecting her until the war with Adrestian comes to an end because she is important to him. Flayn ultimately agrees to that as the two address each other not just as father and daughter - but as Cichol and Cethlenn. Following the end of the war, Flayn disappears while Seteth helps to reestablish the Church's authority in Fódlan - albeit with a new, tolerant stance. After feeling like he's given his message, Seteth joins Flayn in disappearing. It wouldn't be until several centuries - in a Fódlan that's been completely transformed - that the two would reemerge. With the two still dressed in ancient attire, Flayn took a look at this new Fódlan before turning to Seteth and asking if it would be okay for her to call him "father" in this new era. Seteth, however, chooses the safe option.

Part II: Crimson Flower
If Byleth instead decides to ally with Edelgard, Seteth remains at Rhea's side while Flayn leaves Byleth and rejoins her father. The two soon join the knight Gilbert as leaders of Garreg Mach's first line of defense when Edelgard - backed by Byleth and the Black Eagles - launch an attack on the monastery. The two fight ferociously but are ultimately defeated, with the two ordering each other to fall back as they don't want to lose the other. The battle ultimately ends with Seteth and Flayn joining Rhea in retreat as the Empire claims Garreg Mach - at the expense of Byleth going missing. Five years later, Byleth returns and gives the Empire the needed motivation to defeat and capture the Leicester Alliance in the east. Following that, Seteth and Flayn lead a Church force in attempting to retake Garreg Mach. Reaching the outskirts, Seteth vents to Flayn his anger at Byleth for betraying Rhea, even with Flayn reminding her father that they saved her. The two affirm their beliefs that they would be devastated if the other was killed, with Flayn wondering if there could be a way to avoid fighting Byleth. The battle soon begins with Seteth leading the force while Flayn waits in hiding until her father springs the church's trap on the newly formed Black Eagles Strike Force. There are two potential outcomes for them:
 * If the majority of the Strike Force engages either Seteth or Flayn and defeat them, they succumb to their injuries - leaving the other distraught before ultimately being killed, as well.
 * If Byleth engages either of them, they agree to retreat and abandon Rhea should they survive. If they're then defeated by Byleth, both Seteth and Flayn will teleport away. In a letter sent to Rhea after the battle, Seteth reveals the two are going into hiding once again, stating that Flayn's life was more important to him than any vengeance he wanted on Byleth.

Fanon
Seteyn is an uncommon ship in the Fire Emblem fandom. Fans of the ship appreciate Seteth's desire to keep Flayn safe and the lengths he wants to do so. This only magnified when their true identities and nature were revealed. Several fanworks take Seteth's protectiveness of Flayn to it's humorous extreme by making him a helicopter parent that interferes in her attempts at romancing someone. On AO3, this ship has a good amount of support with tagged entries in the 150's range. It's Flayn's most written ship. It's also Seteth's second-most written behind Setleth.

Fandom
FAN FICTION

TUMBLR

Trivia

 * Seteth is unable to instruct Byleth or give seminars during Chapter 6 of Three Houses, where he's stressed about Flayn's disappearance.
 * Additionally, Flayn's and Seteth's support conversation can only be started after Chapter 6.
 * On the Blue Lions and Golden Deer routes of Three Houses, Seteth is unrecruitable in Classic Mode if Flayn was defeated.