Sengoku no Kuroyuri -Futanari Hime to Reizoku no Shoujo- by Kotoba Asobi - Adult Sex Game

Set in the Sengoku period -- a time characterised by warring factions and constant social upheaval -- the story is centred around Oda Nobunaga's sister, Saku. As the princess to Owari Province, she is arranged to be married off politically by her brother to Oumi, in order to solidify the two provinces' ties.

But Saku despises the idea of being married to a man (preferring women in bed instead) and hates the idea of leaving her home province. During an argument over Saku's apparent interest in taking a bride instead of being married off as one, Nobunaga flatly tells Saku that it is preposterous, as two women cannot conceive ch*ldren with one another. In anger, Saku retorts that it is possible, and her brother sarcastically agrees to call the marriage off if she manages to conceive a ch*ld with a woman.