Hotaru Tomoe spends most of her time alone, her weak body limiting what she can do. She's made fun of by her peers at school because of her strange healing power, and has few friends. Few would guess that this quiet girl would possess the spirit of the Senshi of Destruction, Sailor Saturn!
Hotaru is a person that you cannot help feeling sorry for. She spends most of her time alone; her weak physical condition preventing her from doing many things. Her father is always working (Whether for good or evil), and she has no friends because all of her classmates are "grossed out" by her healing ability, or during the "Sailor Moon S" season, are afraid of her hurting them (See below). She's a very shy, quiet, and lonely little girl whose friendship with Chibi-Usa, whom she met about halfway through the "Sailor Moon S" season, brings her so much joy and happiness. As Sailor Saturn, however, Hotaru is very brave and is willing to sacrifice her own life to save those of others.
We are first introduced to Hotaru during the "Sailor Moon S" series, during which she is possessed by an entity known as Mistress 9. Hotaru has no knowledge of this entity, as it inhabited her body after she was killed by an explosion in her father's lab and Professor Tomoe made a deal with an entity (Pharoah 90) to let her live. In exchange, Professor Tomoe was possessed by a daimon and Hotaru by Mistress 9, both of which were key in Pharoah 90's bringing of the Silence. As Hotaru grew, Mistress 9 occasionally took control of her body and hurt those around her, all without Hotaru's knowledge. Unfortunately, this led to all of her classmates to become afraid of her, and Hotaru had no idea why. This continued until Mistress 9 made Hotaru swallow Chibi-Usa's heart crystal, which gave the Messiah of Silence the power to reawaken and completely take over Hotaru's mind and body. The Outer Senshi tried to destroy her, but Sailor Moon wouldn't allow it, because she believed that Hotaru was still alive inside of Mistress 9. Even though everyone else doubted it, Sailor Moon was right, and Hotaru was eventually able to purge her body of Mistress 9 using her power as Sailor Saturn. Sailor Saturn then returned Chibi-Usa's heart crystal, and after a brief conversation with a tearful Sailor Moon, she left to destroy Pharoah 90, even though she would die in the process. Luckily, by combining her own heart crystal with the power of the other senshi, Sailor Moon was able to help Sailor Saturn defeat Pharoah 90 and save her from certain death. Hotaru then was reborn as a little baby, whom Michiru and Haruka returned to Professor Tomoe, who had been purged of the daimon that controlled him.
This was not the end of Hotaru's story however. At the very end of the "Sailor Moon SuperS" season, Setsuna came to Professor Tomoe and took baby Hotaru away to live with her, Michiru, and Haruka. When Galaxia released Queen Nehlenia from her prison, Hotaru began growing at an alarming rate. One night, the spirit of Sailor Saturn came to Hotaru and returned all of her memories from the "Sailor Moon S" season. Hotaru then came before the other Outer Senshi, appearing at the same age she had been during the "Sailor Moon S" season. She spoke of their princess (Serenity) being in danger, and powered Setsuna, Haruka, and Michiru up to the super senshi level. They then left to join the Inner Senshi and Sailor Moon in their fight against Nehelenia, and eventually, Galaxia.
During the Silver Millenium, Hotaru was a princess like her fellow senshi: the Princess of Saturn. However, she was never seen in the Moon Kingdom, for she was given the task of destroying civilizations. When Queen Metallia and Queen Beryl attacked the Moon Kingdom, it was because she had brought her Silence Glaive down upon the kingdom and sealed its fate. However, she was killed during this attack, and was reborn on Earth along with Princess Serenity and the other senshi thanks to the power of Queen Serenity.
In the 30th century, during the reign of Neo-Queen Serenity and King Endymion of Crystal Tokyo, neither Sailor Saturn or Hotaru are known to be living in Crystal Tokyo. Some assume she left Earth with the other Outer Senshi after the battle with Galaxia and returned to Saturn to continue with the duty she was assigned during the Silver Millenium.