@elevown
Fates Birthright and Revelation actually does have one option for a GxG romance (Rhajat) and the upcoming Three Houses is speculated to have more.
As far as Heroes, supports are just a silly game mechanic with some stat boosts. Any two characters can S rank each other and get what appears to be a marriage scene complete with blushing. And by "any" two characters, it can literally even be two versions of the same character, or mortal enemies.