Rozalin is Going Commando
Adell isn't wearing a tieRather, that's a part of his body. If you'll notice, his parents are also wearing ties, despite their shrouded-and-masked appearance and it being incongruous for ALL of them- one would be a coincidence, but all three means there's some other reason. The only reasonable explanation is that their particular species of demon has a large wattle that looks remarkably similar to a tie. He either thinks its a real tie, that all ties are like that, or doesn't know what real humans look like due to Zenon's curse; presumably he figures it out eventually offscreen postgame.
Yukimaru's children will be half-humanSince Adell pretty much drove out every demon in Veldime, there's only 2 male demons left in Veldime. Both are out of the question for differrent reasons, so in order to rebuild the clan (the bolstering of numbers part), she's going to have to marry a human.