Nephilim simply means "big men of reknown". An elite. A king. A Rockefeller of his time. And they took women at their will.
Why do ignorant people teach that Nephilim are some fallen angels or some aliens? If either of these had sex with humans why did they stop? Are angels still screwing women?
Of course not anyway. Only humans were given the ability to procreate the species. Angels do not have this ability anyway.
And there are no aliens in my humble opinion. We are perfecting right here on earth.
1PS