User blog comment:B214/Question and Answers 3/@comment-25051741-20140630213907

From what I can tell so far, it seems Irina is trying to figure out a way she can get some of that Issie Cake and not become a fallen angel. Of course there is that "Promised Day" thing coming up, but here's a guess:

The Flaggelettes!

During the dark ages a group of monks went from town to town and atoned for their (and the town's)  sins by whipping themselves as they walked and chanted. I'm guessing/hoping that after her sexual desires start causuing her wings to flicker more black than white, Irina decides to seek absolution for her sinful thoughts by having Akeno, wearing S&M leather outfit, whip her with Holy Lightning while she (loudly) confesses her deepest desires! After a session of this, she has received the "Absolution of the Whip" and Irina's wings are all nice and white! Now Irina has a way of being with Issei and not falling. How this get's incorporated into their physical relationship would be one erotic as hell scene! With the right cutaways this could be done without falling into Hentai.