User blog comment:B214/High School DxD EX/@comment-178.156.225.173-20160204150252/@comment-3435913-20160204222003

Issei has 22+ kids in thirty years time. 11 have been confirmed:
 * Himejima Kurenai (w/ Akeno)
 * Airi Hyoudou (w/ Asia)
 * Zen Quarta (w/ Xenovia)
 * Shidou Shin (w/ Irina)
 * Ex Gremory (w/ Rias)
 * Robertina Hyoudou (w/ Ravel)
 * Helmwige (w/ Rossweisse)
 * Shirayuki (w/ Koneko)
 * Kurobara (w/ Kuroka)
 * Ernestine Galnstein (w/ Elmenhilde)
 * "?" Pendragon (w/ LeFay) <- first name never confirmed.