Season 1

The first season covers the basics: Tsukino Usagi (Serena) discovers that she's Sailor Moon and goes about the task of collecting the other Inner Senshi (soldiers), Sailors Mercury, Mars, Jupiter and Venus. (Venus, by the way, is the original Senshi. Before making the scene in SM, she was a character in her own manga (comic), Codename: Sailor V. Sailor V is well known to the Senshi, and they regard her as a hero. When Venus first appears, they think she is the Moon Princess. Sailor Moon is a spin off of Sailor V.)

Luna, Usagi's talking cat and protector, tells her they are searching for the mysterious ginzuishou (Silver Imperium Crystal) and the Moon Princess. Unfortunately, they aren't the only ones: Queen Beryl of the Negaverse is looking for the ginzuishou as well. To do this she employs the services of four shittenou, or Dark Kings: Jadeite (Jedite), Nephrite (Nephlyte), Zoisite (Zoycite) and Kunzite (Malachite). They each use different schemes to collect energy from humans that will be used to awaken their leader, Empress Metallia.

Zoisite and Kunzite have a slightly different mission, however: Beryl puts them in charge of finding the nijizuishou (Rainbow Crystals) that will be used to form the ginzuishou. Tuxedo Kamen (Tuxedo Mask), a mysterious masked stranger who shows up at all of the Senshi's battles, is also after the nijizuishou. Luna thinks he might be an enemy, but Usagi fights this idea tooth and nail; she's in love with him, you see.

Things progress, and it turns out that Tuxedo Kamen has several of the nijizuishou, Zoisite has a couple, and the Senshi have, like, one. I don't know. Anyway, Zoisite offers a deal: Tuxedo Kamen brings his nijizuishou to Tokyo Tower and they duke it out. Winner takes all. Tuxie agrees, but somehow manages to end up taking Usagi, as Sailor Moon, with him. She realizes that Tuxie is Chiba Mamoru (Darien Shields), a boy she hates, and he realizes that she is Tsukino Usagi.

Beryl ordered Zoisite not to hurt Tuxedo Kamen, but he defies those orders and stabs Tuxie. Sailor Moon has just realized that she loves him, and she runs to him and cradles his head. He says (in the English version), "I want you to know I've always been on your side." He's dying, she's crying, and her tear becomes the ginzuishou. They both float up into the air, and it's revealed that she is Princess Serenity of the Moon and he is Prince Endymion of Earth. They reach for each other, but Kunzite appears and takes Endymion away.

Things progress from there; Beryl brainwashes Endymion, and he shows up to fight the Senshi, throwing black roses instead of Tuxedo Kamen's usual red. The Senshi travel to the Negaverse to take Beryl on, and while there they run into Kunzite. He opens a portal to transport them "somewhere in time," and they end up on the Moon. They see a hologram of Queen Serenity, and she tells them the story of the Silver Millennium.

Newly empowered, they return and kill Kunzite (indirectly; he basically does it to himself). They then travel to Antartica, where the big bad Negaverse base is located. A battle ensues, and all the Senshi besides Sailor Moon die. Luckily, however, Sailor Moon is able to use the power of the ginzuishou (and the power the Senshi loan her, despite their less-than-living status) to defeat Beryl and Metallia and rescue her Prince.

Everyone dies (except the cats), and Usagi's dying wish is for everyone to have a normal life. They are reborn in their old lives with no memory of being the Sailor Senshi.

For more information about the Negaverse/Dark Kingdom Shittenou, please go to Annabelle's Bin of Rotten Bananas.