User blog comment:B214/Light Novel Volume 16 spoilers/@comment-23853100-20131019035942/@comment-9339850-20131019235418

well if you think about it, Akeno is Rias' childhood friend also and she fell in love with Issei, and Rias went along with it; So Sona falling for Issei isnt that unlikely, but what would be interesting is the circumstances that she falls in love with him, cause i dont see her being in any trouble that Issei would somehow help her with that she cant solve herself