I'm trying to conceive with my wife, so I've stopped masturbating. Azu Amatsuki, my wife's younger sister, tempts me and makes me fully erect! But she makes me cum countless times with persistent stop-and-go blowjobs that only touch the tip of my penis, teasing me with her tongue! She won't let me cum, saying "Do you want me to take it?" and "You don't have to make a baby with your older sister!". My dick goes crazy from the stimulation, and I cum without a partner countless times, becoming a useless cum machine! Ah... both my attempts to conceive and my head are ruined...