Usagi Tsukino è una normale ragazza giapponese che frequenta la seconda media, piagnucolosa e un po' goffa, come lei stessa ammette, la cui vita subisce un cambiamento radicale il giorno in cui incontra una gatta parlante di nome Luna. Questa le spiega che lei è destinata a diventare una delle Guerriere Sailor paladine della giustizia, per salvare il mondo dalle forze del male e al contempo trovare le sue compagne e la Princess.

La sua prima missione risulta esser quella di aiutare la sua migliore amica Naru Osaka, e sua madre proprietaria di un negozio di gioielleria; impara così ad utilizzare i suoi nuovi poteri per combattere i nemici in battaglia, che vogliono impossessarsi dell'energia (energia vitale nell'adattamento italiano) degli esseri umani. Ma ecco che nel momento di maggior difficoltà viene salvata dal misterioso Tuxedo Kamen abbigliato in smoking e cilindro, di cui immediatamente s'innamora.

La Queen Beryl del Dark Kingdom manda il suo servitore Jadeite sulla Terra a raccogliere l'energia degli esseri umani, questo per poter risvegliare dal suo sonno la grande Queen Metaria. Questi tramite un negozio di cartomanzia attira ed inganna un gran numero di persone desiderose di andar a farsi legger la mano e conoscer il proprio futuro, e mediante l'uso della carta del diavolo li rende servitori del male e ad essi ordina di esaudire ogni loro desiderio

Dopo aver osservato lo strano comportamento di alcuni dei suoi amici, tra cui Umino Gurio, che vi si sono recati, Usagi si rende conto che sta succedendo qualcosa di strano e si reca, col supporto di Luna, ad indagare.

Ora Jadeite raccoglie l'energia umana attraverso una spilla a forma di fiore, la flower brooch, che viene consegnata in regalo per posta a coloro le cui lettere d'amore vengono scelte per esser lette al programma Midnight Zero ("Mezzanotte lettere d'amore in diretta" nell'adattamento italiano) dalla stazione radio FM no.10; una delle prime vittime è la professoressa d'inglese di Usagi, Haruna Sakurada, e poi la stessa Naru. Luna scopre il pericolo e convince Usagi ad indagare

Trasformatasi grazie alla "penna magica", la penna del cambiamento (penna lunare nell'adattamento italiano) in una conduttrice radiofonica e riesce ad entrare nella stazione radio: dopo essersi trasformata in Sailor Moon si troverà a dover combattere contro Jadeite; per fortuna proprio nel momento in cui si trova più in pericolo compare Tuxedo Kamen ad aiutarla come al solito.

Usagi è ingrassata di qualche chilo e gli è venuta l'ossessione del peso. Jadeite apre una palestra (palestra con salone di bellezza nell'adattamento italiano), la Shapely (Beauty Gym nell'adattamento italiano), che si occupa principalmente di far perdere peso in brevissimo tempo; in realtà si tratta d'una trappola appositamente escogitata per attrarre le persone in speciali capsule e rubargli in tal modo l'energia mediante i raggi Shape (raggi rinvigorenti nell'adattamento italiano).

Usagi e gle sue amiche decidono di entrar in questa palestra attirate dalla prova gratuita e per vedere come ha fatto la loro insegnante a perder molto di peso in un giorno solo; Usagi dopo esser fuggita, scoraggiata dalla troppa fatica, tornerò successivamente, pentita, con Luna insieme a Luna e quest'ultima, vedendo la Professoressa Haruna molto debilitata la segue e scopre le capsule. Convinta Usagi a seguirla, e a trasformarsi in Sailor Moon, si confrontano con Jadeite, il quale però stavolta riesce a fuggire dopo aver fatto raccolto una grande quantità d'energia umana, lasciando però Sailor Moon lottare contro gli allenatori della palestra da lui controllati. Gli allenatori controllati mediante un diadema attaccano Sailor Moon che, convinta da una possibile perdita di peso reagisce, e grazie alla tiara distrugge i diademi e libera i malcapitati.

Usagi tries to convince her parents to let her adopt Luna, but her brother Shingo has a great disliking of Luna and slight ailurophobia. Later, a mysterious new pet store opens in town which is selling strange new creatures that put Shingo and everyone else who gets one into a hypnotic trance.

Usagi befriends Yusuke Amade, a jazz musician who is being followed by a Youma, and helps him confess to the woman he loves.

Usagi and Naru both dream of becoming stars like Mikan Shiritori, a graduate from their school. When the girls hear that Mikan is holding a talent contest, they see their chance to achieve stardom.

The Sailor Guardians go to the Dream Land amusement park, where visitors have reportedly gone missing. The team splits into two groups: Usagi and Rei and Ami and Luna. But, much to Rei's frustration, Usagi is more focused on playing than finding the missing people.

Usagi and Ami go to the city to enjoy some shopping, where they find a clock store selling a clock that resembles Luna. Later that day, Usagi is happy to learn that her mother bought the exact same clock as a gift. But that night, the clocks from the store emit a strange light, making Usagi and the rest of Tokyo very impatient.

Several people who take the bus near the Hikawa Shrine have gone missing. Usagi, Ami, and Luna decide to investigate by visiting the shrine. There, they meet Rei Hino, a shrine maiden with strong spiritual powers.

Queen Beryl is increasingly furious with Jadeite for his repeated failures; he starts up a theme park, but the general public notices the large number of disappearances. Usagi and Rei, who is now Sailor Mars, begin their combative friendship.

One of Queen Beryl's youma offers to help Jadeite with his wicked plans. Rei wins tickets on a luxury cruise ship and, since she has no boyfriend, asks Ami to accompany her. A jealous Usagi sneaks aboard after them.

Usagi continues to be attracted to both Motoki and Tuxedo Mask. Threatened with Eternal Sleep if should he fail again, Jadeite confronts the Sailor Guardians at an airport.

Nephrite is appointed as Jadeite's successor and begins selecting individual targets for energy, the first one being Naru's friend Rui.

Rei falls for Mamoru and persuades him to go on a date with her, whilst Nephrite targets the caretaker of a local park.

Usagi decides to enter a homemade wedding dress contest, while her home economics teacher is targeted by Nephrite.

Nephrite targets a gifted young photographer, while Usagi tries to achieve her dream of becoming a model.

Shingo upsets his friend Mika, an award-winning doll maker whose skills make her the next target for Nephrite's energy gathering.

Nephrite takes advantage of Sailor Moon's attraction to Tuxedo Mask by sending love letters to Usagi and her classmates. Naru falls in love with him in his civilian disguise, allowing him to drain a large amount of her energy.

Usagi, Ami, Rei, and Luna take a vacation in order to train, but the hotel they have booked is haunted by a strange phenomenon.

Nephrite uses his most powerful Youma to target an animator working for the new Sailor V movie.

Both Luna and Queen Beryl wonder if a visiting princess could be the one the Sailor Senshi has been looking for. Mamoru dreams he is Tuxedo Mask and a girl is asking him for the Silver Crystal. At the ball, Usagi gets her first kiss.

Zoisite decides to use Nephrite's recently discovered romantic feelings for Naru to manipulate him into handing over the Black Crystal to him.

Still in love with Nephrite, Naru becomes an unwilling tool in the power struggle between Nephrite and Zoisite.

Queen Beryl partially awakens the evil entity Metalia and sends Zoisite and Kunzite to find the Seven Great Youma and their Rainbow Crystals. Meanwhile, the tomboyish Makoto Kino transfers into Usagi's school and falls for a crane-game whiz at the arcade.

Naru is still very depressed after Nephrite's death. Usagi and Umino decide to take her to Yokohama to cheer her up. There, a kindly priest is attacked by Zoisite. Mamoru realizes that he is Tuxedo Mask, and drops a locket on the ground, where Usagi finds it.

Ami meets Ryo Urawa, a clairvoyant boy who has a crush on her. However, Urawa's power makes him aware that he will soon be transformed into a Youma by Zoisite.

Usagi and Mamoru are asked to model for the reclusive painter Yumemi Yumeno, who is unexpectedly targeted by Zoisite.

Makoto, like Usagi, develops a crush on Motoki. The two then decide to pursue him simultaneously, even after finding out that he has a girlfriend, who, meanwhile, is targeted by Zoisite and Kunzite.

After fighting off an attack by Zoisite, Rei's grandfather takes on an apprentice and begins acting strangely.

Luna discovers that she has an admirer, in the form of an overweight tomcat named Rhett Butler. Meanwhile, the Sailor Guardians and Zoisite compete for the last Rainbow Crystal.

Zoisite disguises himself as Sailor Moon to lure Tuxedo Mask and the Sailor Guardians out into the open. The Dark Kingdom injures Tuxedo Mask's identity, but they are foiled by the appearance of Sailor Venus.

Mamoru is forced to confront Zoisite in a duel over the Rainbow Crystals, but Usagi inadvertently becomes involved.

Usagi and Mamoru remember their former lives as Princess Serenity and Prince Endymion. The Dark Kingdom kidnaps the injured Mamoru, but Queen Beryl executes Zoisite for his attempt to kill him. Luna and Artemis tell the Sailor Guardians about their tragic past.

Minako tries to cheer Usagi up by taking her to a hair salon, leading to the discovery that Tuxedo Mask is still alive, but now very different.

Determined to become more like the princess she is supposed to be, Usagi decides to enlist in Countess Rose's Princess Seminar.

Usagi and her friends visit the Moonlight Course skiing resort, unaware that Kunzite has sabotaged the Moon Princess Contest in order to unmask Sailor Moon.

After discovering that the Moon Princess was once known for her graceful ice skating, Kunzite tries to use this information to trap Sailor Moon. The best skater among the girls, however, turns out to be Makoto. Tuxedo Mask appears to help them, but only because he does not agree with Kunzite's method of involving bystanders.

Usagi and her family visit a hot springs resort, while Endymion is sent to resurrect an ancient legendary monster.

Queen Beryl orders the seven people gathered who had carried Rainbow Crystals, intending to combine them into one huge youma. Ami is determined to protect Urawa. Sailor Moon tries to heal Endymion.

Kunzite probes Sailor V's connection with the Sailor Senshi by targeting Katarina, an old acquaintance of Minako's.

On orders from Queen Beryl, Kunzite and his Youma investigate the rumors of a rift between Sailor Moon and the other Inner Sailor Guardians, who seem to want both the mystical Moon Stick and the Silver Crystal for themselves.

A blast of energy sends the Guardians to the ruined Moon Kingdom, where they meet a hologram of Queen Serenity and learn about their past. Luna and Artemis find the entrance to the Dark Kingdom. Kunzite attacks, but is finally defeated by Sailor Moon.

After defeating Kunzite, regaining their past memories, and discovering the Dark Kingdom's hideout the Sailor Senshi head for the enemy, but they must prepare for the ultimate sacrifice.

With her friends killed, Sailor Moon is transported inside the Dark Kingdom to face Queen Beryl and the brainwashed Prince Endymion.