In Volume 22, Rias was there to allow Issei to be promoted to High-Class devil, during the ritual in which she placed the crown on his head, which made Issei a King. Later the two become engaged when Issei proposes to Rias after her graduation ceremony, making her his first bride.

Do Issei and Rias end up together?

It's the fact that they finally have an actual relationship now. After seasons of misunderstandings and one-sided confessions, Rias and Issei finally confirmed their love for one another by episode's end.

Does Issei and Rias have a child?

Isane is both a Pureblood Devil of the Gremory Clan, and a half-blooded Humanoid Dragon. He is the son of both Issei Hyoudou and Rias Gremory, as well as one of the two eldest siblings of seven children, being the second oldest child.