User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-37899222-20181223041326/@comment-2208155-20181223104930

Vol 19 life 0.. Yasaka admited that she has not been with a man during certain time(kunou father is dead or is stupid and leave them):

https://www.baka-tsuki.org/project/index.php?title=High_School_DxD:Volume_19_Life_0

“Sekiryuutei-sama, for the time being, can you wait until Kunou grows into an adult? If you can’t wait, you could have me live with you…. Ufufufu. After all, Kunou once pestered me about having brothers and sisters. Not to mention that I haven’t had a young man’s bare skin for a while….”

'''I think that the young man mention is not something important.. I doubt that Kunou father was a human..'''