Series My younger sister, who's a serious club member...

My serious, sports-loving little sister retired from her club and her libido exploded! She’s using *me* for "cock-training" instead of sports! After retiring from the team she poured her heart into, she’s got a surplus of stamina and sexual desire—relieving stress by masturbating constantly! But since masturbation alone isn't enough to satisfy her, she unleashes that pent-up lust on me, driving me to the brink of climax over and over again!