User blog comment:TheBlueSlug/Who should issei end up with?/@comment-4823600-20131113224236/@comment-1359322-20131125155041

I doubt Rias can even complain if another girl gets Issei's child first, Rias already knows that Devils have a low birth rate after all. Like Rias and Sirzechs have an age difference of few hundred years old, and Sirzechs and Grayfia only have a son after being married for a long time.