starman (1984) ripoff: ethereal, shapeshifting aliens send one of their own to explore earth. to walk among humans, the explorer borrows human dna and constructs a corporeal form from it, not knowing that the person they're borrowing from is both very fertile and has a raging pregnancy fetish.
the human alien sets about exploring and learning, and quickly realizes their body is driving them to do things-- put things in their primary facial orifice, deactivate for several hours, and, of course, pursue physical interactions with other humans. having zero understanding of human reproduction and the consequences of their actions, they simply let their body do its thing.
by some quirk of their ethereal composition meshing with human biology, less than a month later their belly is already teeming with babies. they still don't fully understand everything that's happening, but they know their body REALLY likes it. when their comrades send a message checking in, the response is simply: "You guys have gotta try this."
They take their human mating companion back to show off the whole process and get everyone in on it
And that's how you get those planets of hot women the 80s was so obsessed with
