but the forbidden 'love' of a (not even actualized) incestuous relationship (and common Asian lit/mythos trope) is a bridge too far?
In your defense, early on we had, apparently, people in the tower believing something like this was going on between Khun and Maria. It also initially seemed as-if Maschenny was Ran's mom, although in that case the wiki says SIU has since clarified they're both the children of some other Maschenny—I would believe that's actually SIU changing his mind and retconning it, but unless he admits that there's no evidence it's true.
IMHO incestuous unrequited feelings won't be the backstory, here, but—that being said—I do think we'll get a fair amount of "relatedness" between the great warriors. Won't shock me at all if, say, Po Pidau Gustang and Lo Po Bia are both related and, like, contentious rivals, won't surprise me at all if Arie and Ari are related somehow, that kind of thing.
Back on topic.
That’s why she never had kids of her own right?
Correct, she (supposedly) never had kids of her own because she never got over her unrequited love for "some guy". Zahard is—by far—the other "most never got over it" great warrior, and to me it seems like SIU having Yeon hung up on the guy who's hung up would be very a SIU thing for SIU to do. That said, and as
@Jammin also notes, with how little we know V makes about as good of a suspect as Zahard, so for now it's very much still an "open case".
Here are a few other wrinkles for me.
One is that, IMHO, (a) Yihwa Yeon is by far the most-"Korean" (or maybe just "Asian")-looking character of the main cast and (b) Arlene and V are by far the most-"Korean" (or maybe just "Asian")-looking great warriors. I mean, if you put Yihwa in Arlene's clothes and draw her from behind, it'd be really, really close (I think). We've seen a bit of maybe-Arlene's face at the hand, and although it's not great quality it's within the range of "resembling Yihwa".
Since I'm already expecting a lot of relatedness, it would make sense for me for Hana and Arlene to have been sisters, cousins, or whatever. I'd honestly never thought of V and Hana as related, but now that
@Jubei_Kibagami suggested it, it's an intriguing possibility: it also has that same "they look...kinda Korean/Asian, I guess" logic going for it, at least. I'll have to think it through a bit more. The one thing about this, offhand, is that unless SIU does go full-incestuousness on us, we can't simultaneously have (a) "V and Zahard" are brothers (or "related"), (b) "V and Yeon" are siblings (or "related"), and (c) "Yeon was in love with Zahard (or V)". All of those are just theories right now, but they're IMHO not mutually-compatible theories.
The other wrinkle is about the flame of Yeon, healing, and all that: as we now know, the flame of Yeon is really our first sight of a "crazy healing power" in the tower. Next-closest thing we've "seen" is whatever Arlene did to preserve Baam's body, and after that...tower medicine-and-healing options seem much more limited and "ordinary" vis-a-vis everything else.
Here's where this gets funky: supposedly V died by his own hand and, supposedly, Arlene tried-and-failed over-and-over...supposedly failing, as we know, b/c of her immortality contract. Throw in (a) a jealous/pining/whatever Hana and (b) the flame of Yeon's insane-tier healing-and-revival powers and...maybe something else happened? Maybe V is alive and well somewhere (resurrected by Yeon, presumably)? Maybe, actually, the contract doesn't prevent suicide but Yeon kept reviving her rival? Even there her motives could vary—perhaps revival is punishment for her rival, perhaps revival is a favor for the target of her affections (Zahard)? Note, too, that even with this unrequited setup there'd be enough time for a change of attitude: if Yeon has an unrequited love for Zahard, she may have become disgusted with him due to his post-kingship personality shift, murdering of Arlene's babies, and so on—still pining, but pining for his redemption and original personality, perhaps.
towerofgod.fandom.com