thinking about afofa in a royal au and zen would definitely make the "need to keep the bloodline pure" excuse to marry yoichi even though zen doesn't really care about keeping it in the family he's just a brocon
i honestly think he'd give his and yoichi's relationship a different meaning or title—something stronger than a bond of marriage—even in a royalty au scenario.
and also, i think, more importantly, marrying someone also kind of insinuates that one half of the union needs and wants something from the other half, which—to afo—is a big no-no lol.
personally what i find about zenichi so compelling is how afo denies how much yoichi affects him. take that however you want but we only ever hear afo admit how much he needs yoichi at the very end. so afo's denial is unquestionable.
afo tells himself that he doesn't need or want anything from yoichi. he denies this part of himself from thinking that. he doesn't expose this need/want bc of the deep (like, deep deep deeeeeeeep) underlying fear of yoichi rejecting him. he copes with this fear (afo -> bc i don't fear anything who the hell do you think i am) by saying that yoichi is already his and he owns him so—going back to royalty au—why even bother with marriage?
i think with royalty au the locking away in a tower or shut away in an ornately decorated room in an estate with mile-high wrought iron fences is the best route HA
imagine, zen and yoichi coming from poverty, maybe orphaned from some war, zen equates a lavish lifestyle to happiness (simply put, zen remembers yoichi smile when he gave him food/clothes/etc. when they were children) so zen works his way up to rubbing elbows with noblemen whatever means necessary so he can shower yoichi with all the things ever so he wouldn't have a reason to leave (but we all know how that goes!)
