User blog comment:B214/Question and Answers 2/@comment-4547267-20140319005102/@comment-9339850-20140319040651

I think it'd be fine. The engagement ceremony that Rias and Issei went through was basically just testing them. So while they are "technically" engaged, they are also somewhat not; and im sure Rias would want Issei to actually propose to her than just have it be declared by the family