One day, Usagi Tsukino, clumsy 2nd-year middle school student (8th grader), stumbles upon a talking cat named Luna. Luna tells her that she is destined to be Sailor Moon, "champion of love and justice", and she must search for the fabled Moon Princess. Usagi finds friends that turn out to be destined senshi as well, and together they fight to save the world from the certain doom brought upon by the Dark Kingdom (Queen Beryl, the generals, Metallia).
As Usagi and her friends begin high school, a mysterious force releases Queen Nehellenia from her mirror, encouraging her to take revenge on them.
While Queen Nehellenia continues to exert her evil influence on the earth, the rapidly aging Hotaru re-awakens as Sailor Saturn.
People all around Tokyo, including Mamoru, become entranced by mirrors. Usagi remembers a shadow she saw in Mamoru's mirror, and races off with the other soldiers to find him.
Sailor Moon is left devastated after seeing Mamoru get abducted right before her very eyes. To make matters worse, Nehelenia's action is starting to cause a time paradox, which threatens to end Chibiusa's existence.
Sailor Moon runs off to save Mamoru from Nehelina alone. The rest of the Sailor Guardians try to go after her, but one by one they fall victim to Nehelina's traps.
Sailor Chibi Moon and Sailor Saturn make it to Nehelinia's palace, where Mamoru is being held prisoner. But despite their best efforts, the two Guardians are unable to free him, and Sailor Chibi Moon fades from existence.
Mamoru tells Usagi that he's accepted an offer to study abroad in the U.S., which will force them to have a long-distance relationship. Saddened at first, Usagi eventually decides to root for her boyfriend's dream and sends him off with a smile.
Usagi runs into Seiya again and is annoyed by his cocky attitude. The next day, she is surprised to find that Seiya and the rest of the Three Lights have transferred to her school.
Minako decides to work for the Three Lights as their personal assistant thinking it will help her quickly get into the entertainment industry. But Minkao soon realizes that being a star isn't all fun and glamor.
The Three Lights are rehearsing for their upcoming musical, which they will be starring in. But they seem to have a hard time winning the approval of the stage director, especially Seiya, who feels that he is being personally tested.
Ami invited Taiki to come and watch the Wataru's Comet pass by Earth with their science teacher, Amanogawa, only to be rejected.
Yaten temporarily adopts Luna.
Taiki asks Makoto to appear on a cooking show with him. Usagi decides to tag along, but her clumsiness creates a huge mess at the TV studio.
Usagi and the girls try to buy tockets to a Three Lights concert, only to learn it is already sold out. Michiru then passes by and gives them the tickets, revealing that she will be performing with the Three Lights.
Seiya asks Usagi on a date, to which she reluctantly agrees. Sailor Iron Mouse attempts to make up for her recent failures by going after Seiya's star seed.
Usagi and Lina encounters a little girl who appears to be lost. The two later return home that day and are surprised to find the same girl now living in Usagi's house as her younger sister.
Over the summer, the girls go camping in the mountains, where they run into the Three Lights, who are there shooting for an upcoming film.
When Usagi is home alone, she invites Seiya over. The other Senshi and some surprise visitors show up as well!
Taiki begins to question if their activity as the Three Lights is really helping with their goal of finding their missing princess. His frustration continues to grow, to the point where he no longer feels like singing.
Lately, Chibi-Chibi has been coming home with a lot of snacks. Curious to know where she's been getting all the snacks from, Usagi and the girls decide to follow Chibi-Chibi around for the day.
Usagi finds herself teamed up with Seiya for the annual school softball tournament. To make matters worse, Isagi becomes a target of Seiya's fans, who think she is hitting on him.
Sailor Aluminum Siren learns that Usagi is Sailor Moon. Using this knowledge, she sets a trap on a plane where the Three Lights are holding an in-flight event in order to get Usagi's attention.
The Inner Senshi and the Starlights learn each others real identities, but distrust each other, Usagi and Seiya try to bring both groups together.
Seiya and Usagi try to stay together after the Outer Senshi and the other two Starlights forbid them from seeing each other.
Ami and the others try to clear up the misunderstanding the Three Lights have about Usagi but are unable to get in touch with them. As a last resort, the girls decide to enter a video game tournament where the winner gets a chance to speak with Taiki.
Minako is close to realizing her lifelong dream of become an idol after making it to the final round of auditions in a talent-search contest. But Minako is now thinking of turning down the offer, as she cannot ignore her duty as a Sailor Guardian.
Usagi and her classmates are all busy preparing for the upcoming Juban School Festival. Meanwhile, Sailor Lead Crow finds a note left behind by her deceased friend Sailor Aluminum Siren that contains information on Sailor Moon's true identity.
Princess Kakyu, the missing princess whom the Star Lights have long been searching for, finally appears before the Sailor Guardians. Princess Kakyu explains that she has come to Earth in search of the Light of Hope.
Usagi finally confesses to Rei that she has been unable to get in touch with Mamoru for the past several months. Meanwhile, the Three Lights publicly announce their intention to disband their group.
Princess Kakyu perishes after being defeated by Galaxia. Devastated, the Sailor Star Lights go after Galaxia to avenge their fallen princess. Meanwhile, Sailor Moon and the rest of the Guardians also prepare for their battle to protect the galaxy.
Sailor Mars, Mercury, Jupiter, and Venus lose their star seeds after shielding Sailor Moon and the Star Lights from Galaxia's attack. The four Outer Guardians entrust Sailor Moon to the Star Lights while they try to stop Galaxia.
Uranus and Neptune have turned against the Sailor Guardians by swearing allegiance to Galaxia. Despite Sailor Moon's desperate plea, the two continue their attack, forcing Sailor Moon and the Star Lights to retreat.
Galaxia is revealed to be the Legendary Sailor Guardian who sealed away Chaos long ago. However, she has since become corrupt and has gone to conquer the galaxy herself.
As Galaxia closes in to take Sailor Moon's star seed, the Light of Hope finally reveals itself. Turning into a sword, the Light of Hope begs Usagi to use its power to stop Galaxia, who is now fully consumed by Chaos.