Usagi Tsukino is an average student and crybaby klutz who constantly scores low on her tests. Unexpectedly, her humdrum life is turned upside down when she saves a cat with a crescent moon on its head from danger. The cat, named Luna, later reveals that their meeting was not an accident: Usagi is destined to become Sailor Moon, a planetary guardian with the power to protect the Earth. Given a special brooch that allows her to transform, she must use her new powers to save the city from evil energy-stealing monsters sent by the malevolent Queen Beryl of the Dark Kingdom. But getting accustomed to her powers and fighting villains are not the only things she has to worry about. She must find the lost princess of the Moon Kingdom, the other Sailor Guardians, and the Legendary Silver Crystal in order to save the planet from destruction.

The maid Lilith, hired to look after young Yuuri and his family's mansion, seems highly suspicious: she is too good to be true. Every dish she serves turns out to be delicious, the whole residence sparkles after she cleans it, and all the clothing has given off a pleasant scent since she started doing the laundry. Furthermore, her devilishly beautiful eyes only serve to heighten Yuuri's suspicions. Is Lilith perhaps a witch or a sorcerer? Yuuri cannot figure it out. But despite his misgivings, Yuuri has to live with Lilith as he tries to unravel the mystery behind her otherworldly charm.

Usagi Tsukino is still struggling to balance her home life with the duties of being Sailor Moon, the guardian of love and justice. Along with the other Sailor Guardians and her boyfriend Mamoru Chiba, they begin investigating cases of students from Mugen Academy, a school for the most elite students, who are being transformed into monsters. During the investigation, they meet three strange individuals: Haruka Tenou, a handsome racecar driver; Michiru Kaiou, a talented violinist; and Hotaru Tomoe, a mysterious girl with a weak constitution. As more incidents occur, the Sailor Guardians are met with another surprise—the appearance of two new planetary protectors with motives of their own. Despite the newcomers' questionable allegiance to Usagi and her comrades, they all face a threat from a common enemy: an evil entity who calls himself Pharaoh 90.

Usagi Tsukino and her friends have been living peacefully until they are called into action again as Sailor Guardians, planetary warriors fighting for the peace of the galaxy. Usagi, also known as Sailor Moon, leads their group into battle when a new threat from beyond the stars presents itself: two survivors of an alien race, An and Ail. In order to save the source of their life force, the Makai Tree, An and Ail begin harvesting energy from unsuspecting humans. The Sailor Guardians must stop their plot or face the annihilation of Earth. But as one threat subsides, another follows—this time in the form of a little girl from the future who seeks the source of Sailor Moon's power to save her family. However, she is not the only one vying for it, as a group known as the Black Moon Clan also wishes to obtain the power and use it for nefarious purposes. In order to protect their destinies and the harmony of the universe, Sailor Moon and the rest of the Sailor Guardians must fight to stop these forces from succeeding.