Hotaru is a strange, sweet and lonely girl (at
least at first). She lives with her father Souichi Tomoe
in the start, till Setsuna takes her with Haruka and
Michiru and the three of them raise her.
Hotaru's life is difficult. First of all, her mother died, and she herself died. So her father contacted an evil alien (?) and it gave her new life, but possessed. Years later, she met Chibi-Usa, and afterwards transformed in the entity that had possessed her, Mistress 9. That made Sailor Saturn's power awake in her, so she was turn into a baby after destroying the main evil with Sailor Moon's help. Then, she grows rapidly being raised by the Outer Senshi, and died and came back to life... ? Her best and first friend is Chibi-Usa, because she was the only one who didn't got frightened by her healing powers. She met her when Chibi-Usa's hat fall near her.
Her name means Earth Firefly, which explains her hobby (lamps), but Saturn in Japanese is called Soil Star. Though, her powers are not related to soil but to silence and death. She uses her weapon (glaive) in all her attacks. In SailorStars she transforms into Super Sailor Saturn.