User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-74.110.108.150-20141120150126/@comment-1359322-20141120205310

4th girl. Since neither Akeno or Koneko has kissed Issei on the lips yet. The girls that have kissed Issei in order of sequence are:
 * 1) Irina
 * 2) Rias
 * 3) Asia
 * 4) Xenovia