Koakuma Setsuko no Himitsu

One day, high school student Setsuco Yukaribe discovers that she has grown a tail and that her ears have become pointy. Moreover, her sex drive has dramatically increased! Unable to control her lust, Setsuco begins a sexual relationship with her childhood friend, Yuji Tadano. Even though Yuji is initially ecstatic, Setsuco continues to be more demanding, and he finds it increasingly difficult to satisfy her perverted desires.