Buka no Tsuma to Imouto o Netoru Oji-san

This is a story about a single man named Takakura Takeshi, who has Kutsuragi Keiichi, a married man who is the sales manager of a major construction company, as his subordinate. Takeshi leads a double life - on the surface, he is dedicated to his work, but in secret, he enjoys a lifestyle filled with womanizing. One day, after a successful business deal, Takeshi and Keiichi decide to have a small drinking party together. Keiichi, who can't handle his alcohol, gets drunk, and Takeshi takes him home. At Keiichi's home, they are greeted by Keiichi's wife, Kuzuki Yukina, who was once Takeshi's subordinate, and Keiichi's sister, Kuzuki Mako. Takeshi becomes attracted to the mature Yukina and the bright and cute Mako. He starts to have twisted thoughts about seducing both women without Keiichi's knowledge.