UD-636R - My sister is teaching me how to be a man because my wife is cheating on me

Kanako, a woman with an insatiable libido, continues her affair with her former boss despite having a kind husband. When the husband reveals this to his older sister, Reiko, he breaks down in self-blame. Reiko, who has raised her younger brother like a mother since their parents died, feels responsible for his weak and submissive nature. Determined to fix him, she decides to take matters into her own hands and begins giving him 'sexual guidance' to turn him into a real man.