User blog comment:B214/Question and Answers 2/@comment-74.110.105.73-20140222151747/@comment-24501441-20140222170454

I thought that whole thing was hilarious. Both Rias and Issei were oblivious to what was going on. Rias knew it was engagement ceremony, but had no idea that the Maou's were the satan rangers, and Issei knew who they were but had no idea what the ceremony was for. It shows how perfect they are for eachother.

@Tanktung.dang It kinda makes sense that Rias wouldn't know who they were. Her whole life, the 4 Maou's have been the leaders and the most powerful devils in the underworld and Grayfia has always been super strict and formal. For her to come up with the conclusion that they would be cosplaying and doing some rediculous poses may have been a little too much for her to grasp :)