I thought incest within the yukkuri kingdom is generally frowned upon, or is there an exception here?
IIRC, Yuuka's are sort of an exception, since Yuuka's don't usually have an accessory of some kind, other Yukkrui oft consider them to be 'strange' and 'uneasy'. However, because they don't have accessories to begin with, they don't seem as 'uneasy' to other yukkuri as an yukkuri that lost its accessory would be. Thus, they don't usually trigger the "Punish the Uneasy Yukkuri" reaction in normal yukkuri, but are still often ostracized/barely tolerated by the common types. As such, they kinda breed within their own type outta necessity. Or at least, that's what I gather, from my time on here....
As far as literal incest is concerned, not many works have touched on it, but it seems to be 'acceptable' in yukkuri society? It at least seems to be considered more 'acceptable' than mating within a yukkuris own type....