Season 1...Sailor Moon...
Sailor Moon is about a klutzy, crybaby, 14-year-old junior high school girl Serena/Usagi. She recieves special powers from a talking cat named Luna. Her powers help her in her quest to fight evil and find the Moon Princess. With a locket Luna gave her, Serena turns into the sailor suited pretty soldier Sailor Moon. Over time, she discovers other Sailor Scouts/Senshi and another cat named, Artemis.
She also runs into this guy named Darien/Mamoru and this capped super hero named Tuxedo Mask/Tuxedo Kamen. Concidentally enough, they happen to be the same person. Tuxedo Mask/Tuxedo Kamen appears constantly to save the Sailor Scouts/Senshi from the generals of the Negaverse/Dark Kingdom who, at first, begin stealing life energy out of people, then attempt to acquire the Imperium Silver Crystal/Ginzuishou. At this point Sailor moon learns about the Silver Millennium/Moon Kingdom.
A thousand years ago the Moon Kingdom existed and the Universe was at peace. The Moon Kingdom was ruled by Queen Serenity, until the evil forces from the Negaverse/Dark Kingdom decided to try and take over our universe. Queen Serenity was able to repel the invasion, but only by sacrificing herself and sending all of her court and the Imperium Silver Crystal/Ginzuishou to the future on Earth.
This is important because much to everyone's suprise we discover that Serena is the reincarnation of The Moon Princess, Princess Serenity/Princess Serena in addition to just being Sailor moon. It also turns out that the Sailor Scouts/Senshi are reincarnations of the guardians of the Moon Kingdom, and that Darien/Mamoru is a reincarnation of Prince Darien/Prince Endymion, who was to marry Princess Serenity/Princess Serena. This adds a bit of romance to the series, but in the end, the Imperium Silver Crystal/Ginzuishou to annihilate the Negaverse/Dark Kingdom, but at the cost of their own lives.
Note: In the DIC translation, no one dies. Everyone just has their memories erased. Reportedly, the oringial makers of the series weren't sure if they were going to do a second season, and so they wanted to potentially end off the series with a bang. The way this works in the original is that the Sailor Senshi die, but their alter-ego secret idnetities live on to have a chance at a normal life.