Nee, Chanto Shiyou yo!

My name is Kuya Hiiragi. I have six elder sisters. The eldest, Hinano, looks youthful and hates being treated like a child; the second, Kaname, is a famed 'icy lawyer' and my first love; the third, Serori, is a half-Japanese, half-North European beauty with a mature body but childish ways; the fourth, Tomoe, seems stern but is gentle and gets teased; the fifth, Takane, is domineering and treats me like a servant; the youngest, Umi, dotes on me. Adopted as a child, I was sent away to be raised strictly. When I finally returned home, excited to see my sisters—especially Kaname—she raped me that very night, treating me like a toy. Ashamed, I resolve to train my sexual skills, with help from the other sisters, to turn the tables on her. (Source: AniDB)