My Brother's Weird Love Mio Shinozaki.

The older brother doted on his younger sister Mio. When she learns that Mio has found someone she likes, her brother becomes furious and increases his surveillance of Mio. When she learns that Mio masturbates every night, she asks him questions and reveals her own desires and genitals! And while Mio's heart was stolen by another man, he succeeded in stealing her delicate body...