User blog comment:Cookievalenzuela666/harem predictions......./@comment-79.45.189.189-20140329020354/@comment-24468758-20140329115457

Ever since Vol.4 Issei started to be treated as Rias future husband by Sirzechs and the rest of the Gremorys started to do so at least in Vol.5 as he is even called young master.

The ceremony in the ruins of connection is in my opinion the Gremory's tradition for engagement, so you can become engaged without it but you have to go through it before the wedding if you want to marry into the Gremory clan. And as it is a tradition Rias' parents wanted Rias and Issei to go through the ceremony as everyone already knew that they loved each other so Rias consented. In comparision Rias would have never agreed to go through it with Riser unless she would have been forced to.