User blog comment:B214/Question & Answers 5/@comment-24098614-20150707070424/@comment-1359322-20150709001600

@anon, actually no, Rias is still the person to replace Lord Gremory before Millicas, so if Rias and Riser were to marry, Riser would have been the one to enter the Gremory. Remember there are also clans where they are only daughters like Agares or Sitri. So the gender isn't really relevant.