Usagi Tsukino is a 14-year-old schoolgirl who is very cheerful, but clumsy and is always finding herself into unwanted trouble. One day, Usagi meets a talking black cat named Luna, who reveals that dark forces are threatening the lives of the innocent and that Usagi has the power to stop them. Using a magical brooch, Usagi is transformed into Sailor Moon, the chosen guardian who fights for love and justice.

Usagi is shocked to find out that she's gained weight from too much eating. Determined to get back into shape and fast, she and her friends join a gym that advertises instant results for its members.