The 'Fault!!' series plunges viewers into the debauched activities of a high school tennis club that serves as a front for unrestrained sexual exploration. The story centers on Shuichi Sugiyama, who starts by engaging in a passionate, incestuous relationship with his horny stepsister, Mio. Their secret fucking sessions are soon discovered by his tennis partner, Ai Saeki, whose initial shock quickly turns to lustful curiosity. She joins their illicit encounters, escalating their duo into wild threesomes where they explore every hole. The depravity spreads like wildfire through the club as other female members and even their busty teacher are drawn into the carnal chaos. What begins as secret fucking evolves into brazen, all-out orgies on the tennis courts and in the clubhouse. The series arc follows their complete abandonment of sport in favor of relentless, group fucking, showcasing a variety of pairings, hardcore gangbangs, and cum-drenched climaxes where every girl gets fucked senseless by Shuichi and the other male member, Isuke.