why do you think some people pretend Rhea isn't Seteth's younger sister?
Headcanon and the sheer nature of transformative works?
I mean, we do not have a script telling us Seteth is Rhea's older brother. We have a script saying Rhea is the last (in youngest) Child of the Goddess.
Seteth and Flayn are called Children of the Goddess.
Logically, Rhea cannot be the youngest if Flayn exists, so it's widely accepted Rhea intended to say youngest child Sothis created. Flayn wasn't created by Sothis, she was born to her mom and Cichol.
As to what is Seteth's relationship to Rhea, I'm 300% under the "he's her tired big bro" theory, as to why people make him younger than her...
Maybe because he acts as her second - a role often given to younger siblings? Or, for certain people, if Seteth is younger than her, then "he had no choice but obey" her various orders when she's obviously "bad" - ditto for the "they're not siblings but cousins" or something like that. Or just, because it isn't explained anywhere and for those people it'd make more sense to HC as cousins than siblings - everything is HC in Fodlan after all, the devs didn't care about their own lore.
I personally like the subvertion of "big bro supports lil'sis being a leader" instead of the traditional "big sis supports lil'bro being a leader" seen and re-seen in Archanea and Jugdral.













