User blog comment:B214/Question and Answers 3/@comment-3965848-20140620151612

We all know that each girl in the harem had thier reason for falling for Issei


 * Rias: for saving her from her engagement and seeing her only as "Rias"


 * Asia: for being her first friend and going farther then anyone to save her


 * Akeno: not having any problem with her FA blood helped with her relationship with her father


 * Ravel: being the hero she admired


 * Xenovia: admired how strong, brave and kind he is


 * Koneko: helping overcome her fear of senjutsu


 * Rosswiesse: seeing him as an interesting person

So what exactly was Irina's reason for it, do you think it will show in vol 18