Baby Hotaru is taken from Professor Tomoe by Sailorpluto. Neherenia crushes the mirror that represents her soul at the promptings of Galaxia's voice. While Chibi-Usa is trying to return to the future, this action prevents her from returning. A shard lands in Mamoru's eye. Chibi-Usa is upset that she is trapped here, but the others tell her not to worry.
Haruka and Michiru are visiting an aquarium. While they are up on the roof, they notice the shards falling, hurting people around them. Haruka gets one in her hand but Michiru removes it. The shards turn into mirror paredories-- shards of glass that look like Neherenia. They're surrounded, but then Pluto's Dead Scream hits them and shatters them. Pluto tells them to transform, and the three of them battle the paredories which have reformed. Uranus is knocked over the edge, and Neptune tries to hold her up while Pluto is held back by a paredory. One tries to attack baby Hotaru, and the Outer Senshi scream at it to stop. The symbol of Saturn bursts into light and the paredory is thrown back. The Outer Senshi receive their Super forms, and defeat the paredories. They turn to see Hotaru-- now looking to be about six years old, and will grow again later.
In the meantime, Mamoru has been acting really odd due to the shard and Usagi is getting worried. She also notices people around school are getting obsessive about mirrors, and so is Mamoru. The Senshi help transform Supersailormoon into Eternalsailormoon until she can do so on her own. Usagi goes to Mamoru's apartment and finds him staring into one and an image of Neherenia appears. Usagi is getting really pissed. Neherenia captures Mamoru, dragging him into her mirror world. Chibi-Usa starts to fade away-- if Mamoru stays there, she can't exist.
The Senshi all go to her castle place thingy using Sailor Teleport, but are separated when they let go of each other's hands. They are split into groups of two each-- sorta-- Moon and Jupiter are on their own though. The groups are each confronted with paredories and are captured in mirrors, except for Saturn, Chibimoon, and Eternalsailormoon.
Saturn and Chibimoon are in the palace while Usagi tries to fight her way to it. Mamoru is lying on the throne, and Chibimoon is clinging to him. Out of nowhere comes a blast from Neherenia, and Saturn deflects it. After exchanging some words, they start blasting each other, and Saturn uses her Silence Glaive Apply, but Chibimoon stopped her before she could complete it though. She fell to the ground blinking out again. Saturn is distracted and captured. Neherenia just laughs and toy with Mamoru. Usagi runs up and gathers Chibimoon into her arms, but Chibimoon fades even more, whispers "Usagi, I couldn't save Mamo-chan. But I believe in you," and then disappears entirely.
Usagi and Neherenia are arguing, and Neherenia says talks about how she wants revenge, and Usagi tells Neherenia to take revenge on her. The shard in Mamoru's eye comes out and the mirrors the Senshi are in burst. Chibimoon reappears. Neherenia gets mad and starts blasting everyone, and Usagi transforms into Eternalsailormoon. Finally, Neherenia breaks down (all she wanted was a friend) and her big mirror breaks and she disappears in a flash of light. The Senshi stand in what remains of her palace, and you hear an evil laugh...
An idol group called the Three Lights gives a concert. The Inners talk about which ones they like; Minako and Makoto like Seiya, Rei likes Yaten (and the other two agree), and Ami likes Taiki and they all agree. They ask Usagi who she likes and she whispers, "Mamo-chan" ^-^. She tells them that he is going to America to study at Harvard for about a year. As they're walking home, Usagi seems worried, and Ami mentions to the others that Chibi-Usa went back to the future. Later, Usagi is sitting on Chibi-Usa's bed holding a picture of them with Mamoru, and Luna comes in. They talk, and we see Mamoru packing, with the same picture. The next day, Mamoru is waiting for his flight, and Usagi is with him. Usagi is crying a bit, and Mamoru takes out a box and gives her a ring. He puts it on her and she's really happy, and they kiss. Then there's a lot of shrieking, and they turn and see some girls piling around the Three Lights. Mamoru gets on his plane and leaves. We see Galaxia, laughing and talking about gathering star seeds. She talks about using them to take over the galaxy. The scene goes back to Mamoru. A huge light rushes at the plane, and he stares in shock. The plane disappears in a flash of golden light. In a later episode, we see that this happened: Mamoru is out on the wing in his Tuxedo Kamen getup, and Galaxia is standing there. He leaps at her and she blasts him, and he falls to the ground. His hat and mask have fallen off. Galaxia took out his star seed, and he says the Sailor Senshi will stop her. Then he disappears, and whispers, "Usako".
Anyway, after they showed the plane disappearing, the Inners minus Minako are in the cafe with Luna. Ami and Mako are embarrassed about Usagi's ring and I think they were talking about it. Usagi says, "What's that?" Rei says, "You really don't know? You're a girl, right? Even Luna knows." Luna says, "I'm a girl." Usagi and Rei start arguing, and Usagi still doesn't seem to get what the ring is. They're interrupted when Minako bursts in babbling about the Three Lights filming something in the park. There's a huge crowd there, and all the girls are really excited, especially Ami (!). They can't see what's going on, and they all start jumping up and down trying to see. Finally, they decide to force their way to the front of the crowd. Rei, Minako, Makoto, and Ami disappear into the crowd, but Usagi is left behind. Behind them, unnoticed in a tree, is a small, white-haired girl wearing a Chicago gangster-style pin stripe suit and sunglasses. Her name is Iron Mouse, and she was sent by Galaxia. She takes the star seed from an idol singer who was there for the filming. Usagi sees what happens and transforms. The idol singer becomes some weird monster-thingy. New senshi called the Starlights show up and are ready to kill her, but Eternalsailormoon stops them and heals the singer. The Starlights disappear. Usagi keeps the incident to herself for awhile.
The Three Lights transfer to the school that she goes to with Minako, Ami and Makoto. They all-- along with Rei-- start hanging out together and become sorta friends. The Three Lights, however, don't appear to get along with everyone... Haruka and Michiru meet them when Michiru is performing a joint concert with them. She and Haruka sense a strange energy coming from them, and vice versa. Seiya and Haruka hate each other as soon as they meet-- Seiya was flirting with Michiru and Haruka got mad. Chibi-Chibi appears and becomes a nuisance, and no one knows who or what she is-- even Setsuna, who keeps popping up out of nowhere when Chibi-Chibi first does.
Through the season, people keep getting their star seeds taken out, several more animamates-- Lead Crow, Aluminum Siren, and Tin Nyanko--appear, as Galaxia tries to find the star seeds she needs. The Senshi find out that the Three Lights are the Starlights, and vice versa. The Starlights' princess that they've been searching for-- Kakyuu-- appears, but her star seed is removed and she dies.
The Senshi go to battle Galaxia. Somewhere around here, Chibi-Chibi becomes Chibichibimoon. The Inner Senshi are killed and die telling Eternalsailormoon and the Starlights that they'll miss them, they have to go on fighting, etc. Moon loses her will to fight. The Outer Senshi go alone to attack Galaxia. Galaxia reveals that she is the one that caused Hotaru's growth spurts since she needed her to be older in order to take her star seed. They are about to be defeated when Galaxia offers a proposal-- she'll give them her bracelets to keep them alive if she can have their star seeds. They'll have to serve her though. Pluto and Saturn tell her she's crazy, but Uranus and Neptune agree. Their star seeds are taken and they accept the bracelets-- and are now under Galaxia's control. Under her direction, they kill Pluto and Saturn. Moon, Chibichibimoon, and the Starlights arrive to see Pluto and Saturn disappear. Galaxia tells Neptune and Uranus to kill them, and they battle the other senshi for awhile. Uranus slaps Moon when she tries to convince them to break Galaxia's hold, and then pummels Starfighter. Galaxia is quite confident in herself. Uranus and Neptune, however, break her hold and attempt to extract Galaxia's star seed. It doesn't work; she doesn't have one. She takes the bracelets away from them. As they lay dying, Uranus tells Starfighter to protect Eternalsailormoon, and holds Neptune's hand as they fade away.
The Starlights battle it out with Galaxia, but she takes out Moon's star seed. Moon is able to get it back somehow, and transforms into this angel-like thing. She gets into a swordfight with Galaxia, who has turned into the incarnation of Chaos. Moon's sword breaks, and it turns out it was actually Chibi-Chibi. Moon manages to get inside Galaxia's mind and find the part inside her that wasn't corrupted by Chaos. She drew the good side out and Galaxia was healed. It turns out that Chibi-Chibi was her star seed, which she sent away so she'd have a chance at being good again. Moon is left drifting alone, then suddenly Mamoru and the Senshi appear alive around her. The Inner Senshi go to a rooftop and say goodbye to Princess Kakyuu and the Starlights as they leave for their own galaxy in the form of shooting stars. The Outer Senshi, sitting in Haruka's car, see them as they leave and make wishes. Later, Usagi and Mamoru are talking together and kiss. That's the end of Sailormoon ;_;