Shota goes to the exercise gym. However, he is obsessed with the instructor Yui's big ass and forgets about exercise! One day, Shota ends up staying the night at Yui's house! He takes the opportunity to get his dick throbbing and play pranks on Yui's plump ass! Before he knows it, his personal training has turned into a blowjob with her big ass sticking out! When they take a bath to wash off their sweat, they start washing each other and somehow end up having raw sex from behind! At night, his precocious classmate bursts in and they engage in a night-time threesome that makes his ass shake! Big ass exercises will eliminate lack of exercise and frustration!