Hotaru goes to Mugen Gakuen with Michiru and Haruka, and she's 12. In the manga, she is in sixth grade. In SailorStars, her age changes dramatically, from being a baby to approximately 4 to about 8. Then she goes to the same school as ChibiUsa in the manga.
Hotaru is a very lonely girl with no friends. She is weak and any physical exercise causes her to collapse. She has the strange power of healing (reiki?), which grosses out the other girls at her school. She lives in isolation with her father, Professor Tomoe, in the Tomoe Mansion; her mother had died when she was 3. Hotaru finally finds a friend in Chibi-Usa, and later the rest of the Sailor Senshi.

While looking at an experiment in her father's lab, and explosion ocurred and everyone was killed including her, except for Prof. Tomoe. Master Paroah 90 then shows up and after hesitation Professor Tomoe joins him and becomes evil in exchange for bringing Hotaru back to life. Then Hotaru becomes possessed by Mistress 9, an evil entity whose job is to steal all the pure crystals and prepare everything for Master Pharoah 90's plan to bring the Silence, putting the world into a cold sleep forever. Hotaru was tricked into swallowing Chibi Usa's heart crystal for power, this is how she became Mistress 9. Hotaru is also referred as the Dark/Anti Messiah. Hotaru eventually prevails over Mistress 9, becoming Sailorsaturn. Then she leaves to destroy Master Pharoah 90 and SailorMoon follows her after becoming Eternal SailorMoon.

At the end of Sailormoon S, Hotaru dies and reborns (all senshi are immortal). Eternal SailorMoon comes back with a baby in her arms, this is baby Hotaru. By then, Professor Tomoe is no longer evil and baby Hotaru is returned to him.

In SailorStars, baby Hotaru is taken from Tomoe by Setsuna, who needs her. Hotaru is the reason for the other three Outers Senshi to power up. After a battle where Hotaru proved her power as a baby by destroying the evil creatures who were trying to kill her, she grows to about 4 years of age. Later, Hotaru grows to about 8 when her Senshi spirit (Saturn) revived all of her memories. Now she is SuperSailorSaturn. In the manga, she can also play the violin, like Michiru.

Transformations

Saturn Planet Power Make-Up
In the Manga only: Hotaru says this to become SailorSaturn.

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Attacks

Death Reborn Revolution
Saturn's attack which would destroy the world. It was never been shown in the anime, but it was in the manga. Saturn raises her Silence Glaive in the air, shouts the words, and thousands of ribbons fly towards her, wrapping around her body.

Silent Wall
A protective move used to block things,like energy blasts. She uses this to protect her and the other senshi from any attack.

Silence Glaive Surprise
An extremely powerful attack that nearly destroyed an entire building in SailorStars. Its full potential was not shown, as SailorChibiMoon prevented Saturn from finishing it by stopping the Glaive before it hit the floor. Saturn raises her Silence Glaive and brings it down in an arc while yelling the words. It produces a moment of silence and then a huge explosion occurs that destroys everything around it.

(Did you find any mistakes? please let me know: Neotokyo_2040@yahoo.com)