In the X-Files Episode "All Souls" (S5 E17), Fr. McHugh tells Scully the story of the Nephilim. In his version, there were four Nephilim, children of a Seraph1 and a human woman, who were not "meant to be," so the Seraph came back to earth to take their souls to Heaven before the Devil could get them. He attributes this story to an unspecified non-canonical work.
I have been unable to find any story about the Nephilim (outside of this episode) in which
The angelic father is specifically a Seraph2,
there are exactly four Nephilim, or
the angelic father is sent to reclaim them.
Is this a real thing? My search results are so full of Supernatural Wiki and Madeline L'Engle criticism that I'm unwilling to take my inability to find it as real evidence. OTOH, there's plenty of other Catholic material in TXF that they just made up.
1 The four-faced angel described by Fr. McHugh is actually a cherub, but I guess that doesn't sound as badass.