The title is so awkward to translate into English so I just did it literally. (If you want the romanji: [Popship] Futanari Manko wo Ore Senyou Onaho ni Choukyou shitatta w
Anyway, please support the artist by buying the work here: http://www.dlsite.com/maniax/work/=/product_id/RJ132206.html
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Story wise, it's something I don't usually see too often. A futanari being NTR'd (though her boyfriend isn't ever depicted, I still consider it NTR since they make direct references to him at points).
A translation of the description on dlsite:
"Hmm... It looks like there isn't any good footage today as well, huh..." One day after school, I was looking through the footage of a camera I hid in a classroom like I always do. I actually wanted to put cameras in other classrooms as well but since I don't have any money, I just spent every day looking through the footage. It had been two weeks without anything interesting so I was thinking of just putting it in a different classroom but as I was thinking that... "Uho! Yu-Yuka-chan!... and a classmate." To think that Yuka-chan would come... The only redeeming thing about this boring school life! An absolutely stunning face! My oasis in the classroom! "Ohoooo! She-she's stripping!" As I thought, she was taking off her clothes. Damnit, to think that the rumors that she was dating this guy were true. I'm extremely jealous but if it weren't for that fact, I wouldn't have gotten this awesome footage! "Ooh! Yuka-chan's boobs are just as huge as I imagined them... Hurry, hurry, take it all off! Take it all off! Ta-...!" Wha-What's this? On the smooth skin that you could recognize as Yuka-chan's even through the camera... The thing on the lower half of her body is...? "Fu-Futanari...?" Are you for real... A dick on the lower-half of a girl... To think that futanaris actually existed... It's shocking... to think that the girl I like was a futanari... "...actually, isn't this my chance?"
Aha, really quick turnaround on this one. There's plenty of recent good stuff out there unposted but it's good to see this one didn't go under the radar.