An explanation plus MAJOR spoilers for “like a moth to burgundy flame”
Sae and Ryusei in this entire series, “Where We’ll Always Belong,” are the same Sae and Ryusei all throughout. However, because of who Ryusei is (if you haven’t read my fic “like a moth to burgundy flame” this is going to be so fucking confusing so i’d really advise you to go read it) they’re able to traverse through different universes. This is also possible for both of them because Sae is no longer bound by a mortal body to her old world (aka the historical fantasy AU).
Ryusei has made it her mission to show Sae not just her world, but as many worlds as possible. These two can and will meet versions of themselves, genderbent or not, in all the AUs and canons in which they exist. Along the way, they’ll revisit their origin universe, because even if there’s an infinite horizon of the new and unfamiliar doesn’t mean they ought to leave behind what makes them who they are—and they won’t, especially not Sae.
Any Ryusae fics not included in this series do not feature the same Sae and Ryusei as this series.