User blog comment:TheBlueSlug/Ending/@comment-13296492-20130725101259/@comment-1359322-20130725101541

It's Rias not Rais. And yes Issei and Rias does love each other, but Issei also have feelings for the girls and the girls love Issei. Rias' understands that fact, so she isn't stopping Issei from forming a harem under the condition that she stays in the no.1 spot.