Wait. Flayn and Byleth are related in someway right? Like distant relatives? If they are related then if you decide to marry her... isnt that like marrying your cousin or something? lol
It's kinda vague. Flayn, is the daugher of Seteth. Seteth is a child of the Progenitor God (Sothis). But whether that is literal in that Sothis is their actual mother versus figurative in it just being a name for their race, isn't particularly elaborated on. Byleth is Sothis reborn, sorta, but even that isn't super literal, so much as Byleth is a host of Sothis's power/personality.
So if we want to be really literal, Flayn is Sothis's granddaughter and with Byleth being Sothis reborn, then Flayn is Byleth's grandaughter. But I don't think that is how the game would like you to see it.
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S*** I have to stop doing that," Gheb said, as he lay back down and died again. - Forgotten Love The Chiefs won the Super Bowl!