As Sailorsaturn, she is not her cheery self. She is the vessel for the entity Mistress Nine, her only goal is to destroy all life on Earth and bring forth the Silence. She also wields a fearsome polearm, the Silence Glaive, which can be used to slice through anything that gets in her way and bring the destruction of the planet. Mistress Nine is brought forth when the Death Busters took Chibiusa's pure heart and tricked Hotaru into eating it. They told her if she ate it her friend would get better. However, at the end of SailormoonS, she overpowers Mistress Nine and they are both destroyed. Hotaru is brought back, however, in the form of a tiny baby (very kawaii!). She is now raised by the Outer Senshi, who she calls Haruka-papa, Setsuna-mama, and Michiru-mama.
Hotaru doesn't appear SailormoonSuperS, it is only in SailorStars when the spirit of Sailorsaturn gives Hotaru her memories back. Hotaru then grows to about the age of 12, but now she fights to save the planet instead of fighting to destroy it. Hotaru, along with Setsuna, dies early in the SailorStars episodes.