Shota attends a fitness gym but rarely exercises, always mesmerized by instructor Yui's big ass. One day, he gets the chance to stay over at Yui's place and immediately takes advantage, his cock hardening as he plays naughty tricks on her firm, shapely buttocks. Personal training time quickly turns into Yui bending over with her ass sticking out, inviting a blowjob. Later, while bathing together, their soapy play somehow escalates into raw doggystyle sex. At night, a horny classmate crashes in, launching them into an intense threesome that makes their asses tremble violently. With big-ass workouts, both his physical laziness and sexual frustration are finally satisfied in one go.