User blog comment:B214/Volume 22 spoilers/@comment-3965848-20160728173904/@comment-9595671-20160729071025

Yeah, it honestly surprises me how we've been given many characters' birthdays, but yet we've never seen anything related to a character's birthday.

I mean it doesn't even have to be Issei's either, it could even be Rias' birthday instead since I'd like to see what Issei tries to think of doing for her.