After Usagi becomes self-conscious about her weight (and with Luna drawing pictures of Usagi looking really fat to tease her) she goes to school and talks to her friends about wishing there was a quick way to lose weight. The students all notice that their teacher, Ms. Haruna, is suddenly looking great. A nerdy guy in their class, Umino/Melvin, has apparently been stalking the teacher and lets the girls in on the fact that Ms. Haruna has been working out at a new gym that just opened.
Again, the rule here is that anytime a trendy new business opens, trouble is brewing.
Usagi, Naru, and a couple other girls from school go to check out the gym and are put to work by a blond gym trainer, "Jed". Usagi quickly decides to ditch gym training and go see her crush, Motoki/Andrew, who works at the arcade. Motoki saves Usagi from fainting (she has been starving herself all day), and convinces her to eat something. Usagi then eats way too much food, freaks out, and decides she must go back to the gym. After an encounter with Darien/Mamoru, a guy who teases her all the time, she returns to the gym and starts working out frantically.
Meanwhile, as the other girls have finished their workouts, Jed convinces them to climb into "relaxation pods", claiming that if they want to lose weight the pods will make all the difference. Of course, the pods are actually stealing energy from the girls, as well as Ms. Haruna. Usagi figures this out, transforms into Sailor Moon, and gives her signature speech. Jed, now revealed to be Jadeite, sends some possessed muscle men after Sailor Moon. Sailor Moon beats them up and then heals them with her Moon Tiara. Jadeite disappears, and Queen Beryl threatens him once again to stop messing up.
Back at home, Usagi's brother plays a trick on her, adjusting the bathroom scale to say that she weighs a lot more than she actually does. Usagi freaks out.