We have encountered many whom have sexual encounters with fallen angels. This is not a new phenomenon as the Scriptures record of this sexual sin being carried out in Genesis 6:1-4:
“Now it came to pass, when men began to multiply on the face of the earth, and daughters were born to them, that the sons of God saw the daughters of men, that they were beautiful; and they took wives for themselves of all whom they chose. And the LORD said, “My Spirit shall not strive with man forever, for he is indeed flesh; yet his days shall be one hundred and twenty years.” There were giants on the earth in those days, and also afterward, when the sons of God came in to the daughters of men and they bore children to them. Those were the mighty men who were of old, men of renown.”
The text refers to the “sons of God,” angels whom had fallen (no pure angel would entertain the thought of marrying or entering into a sexual relationship with a human). These fallen angels entered into unholy unions with human beings, we see this in verse 4, and “…when the sons of God came in to the daughters of men…”
These angelic beings came “in to” daughters and produced human-demon hybrids. I do not believe fallen angels have the capability to reproduce but rather they affected the pregnancies of the women and altered their DNA thus creating a human-demon hybrid. These extreme acts of evil brought upon the wrath of God- the Flood.