Mitsudomoe Darling: Futari no Kare ni Semarare Karada ga Mochimasen

Chihiro Seto has been dating her kind, caring, and popular boyfriend, Kaname Yukishiro, for six months now. The day has finally come for them to move in together. Everything appears to be going well, but the two are yet to go all the way... Both excited and nervous that tonight might be the night, Chihiro receives a reading and a bottle of strange liquid from a street-side fortune teller. Later that evening, Kaname drinks the mysterious potion and falls asleep, only to wake up and see a double of himself! Chihiro is unable to tell them apart, but that doesn't stop their amorous advances... Chihiro is about to receive six months of pent up desire from all angles!

(Source: Renta!)