User blog comment:B214/Question and Answers 2/@comment-117.196.181.215-20140224174554/@comment-1359322-20140225015324

That depends on the individual. Sure Sairaorg wants to become a Maou but that probably won't happen until at least another few thousand years in which that time he'll have to serve as his clan head.

The issue here is clan heads doesn't marry clan heads The issue with the succession of the clans.

Devils have low birth rate, so there might be situations like both clan heads are the only child of their clans, in that case, who should follow who, should the husband follow the wife or the wife follow the husband. And which clan will their child succeed, if they once again only give birth to one child, is it the mother or the father's clan. Either way, which site is chosen, there will be resentment between clans, thus to avoid such issues, Clan Heads and Heirs of their clans don't get engaged or married with each other.