Here is a very brief synopsis of SMS

SailormoonS is a new introduction to power, evil, death, destruction, and rebirth. New Sailorsenshi and heinous villains are introduced. Senshi such as Saturn, Neptune and Uranus, and villains like the Deathbusters.

The Deathbusters are searching for pure heart crystals to awaken the Dark Messiah, Mistress Nine, who is a demon who possessed Hotaru's body but lay dormant until recently. Tomoe's wife and daughter, Hotaru, died in a lab accident and he made a deal with Master Pharoah Ninety to let his daughter live.

Tomoe was possessed by a daimon and Hotaru, with Mistress Nine. Hotaru/M.Nine is given Chibi-usa's heart crystal which awakens Mistress Nine. She obtains the holy grail and calls upon Master Pharoah Ninety.

Mistress is hit by a flood of memories and Hotaru takes her body back, but the ruin has already began. She sacrifices herself to stop the Pharoah and dies. The end of S shows Sailormoon and the senshi together, Sailormoon holding baby Hotaru. The outer senshi take Hotaru with them to care for and raise her. Thus ends S.