Imouto Reiji ~Mileage~

Looking much younger than his age, a young boy (protagonist) was bullied by two girls. It was intolerable to live with the humiliation day after day.
So he spoke to his sempai at work, and the solution was... an aphrodisiac.

"If a woman drinks this, she will think only about c*ck."

Feeling that he would be happy with enslaving just one of the girls, he went about his scheme to drug her...

[From DLsite English]