Fella Pure: Mitarashi-san Chi no Jijou The Animation

On the outside, Keiko Mitarai is absolutely perfect; she has a beautiful figure, astounding leadership, and a good reputation among the students. Unbeknownst to many, however, behind the charisma she exudes lies a complete pervert who cannot stop thinking about the sexual art of fellatio. Because of this, whenever her parents are away, she uses her younger brother to discover new ways of giving pleasure, which is bound to one day go too far.