User blog comment:B214/Volume 17 spoilers./@comment-24588585-20140225001025/@comment-24468758-20140225220814

Rias is the >>legal<< wife and official girlfriend (except for his human life), Asia, Akeno and Koneko are his future girlfriends Issei is just too dense to get it, since he accepted their confessions but he did not deepen these relationships as of now. Rose is most likely becoming his newest girlfriend in this volume. Additionally Ravel is considered part of his harem but has yet to confess to become one of his future girlfriends. Xenovia and Irina are going to join his harem officially in the next volumes and Kuroka and Le Fay are considered to become part of his harem in the future.