Harumi-chan no Oita
It’s the story of a guy who finds a naked girl masturbating in his apartment room. So he does what any other “normal”, straight guy would do: he fcks her.
He eats her out, gets sucked off, goes in virginally, anally, tries some bondage. At first the girl doesn’t understand what’s happening. She doesn’t know why she’s so horny or what sex is. So at first she doesn’t enjoy it but then gets really into it and starts moving on her own. She starts to act weird, her head spins 360°. Her head pops off.
Now here’s the twist: she’s an alien robot made to monitor human sexual behavior.
Two naked humanoid aliens come down to the apartment and rape the guy. End. I love it.
The thing about this guy is, like the guy from Fairy Forest Remi-chan, he starts off as being a pretty normal guy but as the hentai goes on these guys evolve into sick perverts.
This hentai shares the same producer: Adult Source Media.
Same plot: a guy discovers a naked girl, has rough sex with her and there’s a twist ending.
I rate this as very good particularly for the ending.