User blog comment:Jopjopjop/Volume 18 Spoilers/@comment-24331706-20150321134838/@comment-24502975-20150321163254

It doesn't matter if Ise was aware of it or not, Irina's still his first kiss. And considering at the start of volume 19 Ise tries to get Irina not to mention that so loudly, yes, Rias doesn't know.