What SailorMoon R is about.

Tsukino Usagi is an ordinary 8th grade schoolgirl who, one day on her way to school, saves a cat with a crescent moon on its forehead. At home, depressed after having failed a test, Usagi meets the cat again in her room. The cat, amazingly, can talk, and she introduces herself as Luna. Luna gives the dubious Usagi the ability to transform into Sailormoon, the pretty sailor suited soldier of justice.

Sailormoon faces the Dark Kingdom, an enemy group that wants to take over the Earth. The Dark Kingdom consists of Queen Metallia, Queen Beryl, and the four generals: Jadeite, Nephrite, Zoicite, and Kunzite. Sailormoon's mission is to protect the world while finding the Moon Princess whom she is sworn to protect. She finds allies in Tuxedo Kamen, a mysterious masked man who assists her in her fights but has his own agenda (and whom Usagi/Sailormoon has a huge crush on), and the other Sailor Senshi that she gradually discovers in four other girls: Mizuno Ami/Mercury, Hino Rei/Mars, Kino Makoto/Jupiter, and Aino Minako/Venus.

Usagi's main relationship crisis throughout the season consists of her problems with Chiba Mamoru, an attractive but annoying college student who constantly teases her. He is really Tuxedo Kamen, but he (and the Sailor Senshi) don't discover this fact until much later.

The Dark Kingdom's first job is to gain energy for Metallia by draining the life forces of humans. Later on, however, they begin to look for the ginzuishou ("mystical silver crystal"). Eventually this leads them to go after the seven rainbow crystals sealed inside seven people who were originally the Dark Kingdom's seven original youma. When brought together, the rainbow crystals create the ginzuishou. Thus the new priority of the Sailor Senshi is to find the seven rainbow crystals before the Dark Kingdom does. The Dark Kingdom, the Sailor Senshi, and Tuxedo Kamen all vie for the crystals. Eventually because of the crystals, Usagi and Mamoru discover each other's identities when they are trapped together by Zoicite. Usagi is the true Princess of the Moon, and Mamoru is her lover, Prince Endymion of Earth. Usagi receives the ginzuishou, but Mamoru is kidnapped and brainwashed by the Dark Kingdom.

After a whole bunch of filler episodes in which the Dark Kingdom and evil Prince Endymion/Tuxedo Kamen try to get Sailormoon to hand over the ginzuishou, Usagi, Ami, Rei, Minako, and Makoto must confront the Dark Kingdom, learning about their pasts on the moon in the process. In episode 45, Mercury, Mars, Jupiter, and Venus all die trying to protect Sailormoon. In episode 46, Mamoru, as evil Prince Endymion, tries to kill Sailormoon, but before he can finally do so, Sailormoon revives his memories. Mamoru then dies trying to save Sailormoon from Queen Beryl. Sailormoon then defeats Beryl and Metallia as Princess Serenity using the ginzuishou and the other Sailor Senshi's powers, then dies, since that is the consequence of using the full power of the ginzuishou. Usagi's last wish is to live a normal life as a normal girl, so her wish is granted, and at the end of the episode, all the girls and Mamoru come back to life without their memories