Hotaru Tomoe was the last of the Sailor Senshi to realise her origins, when she became Sailor Saturn, Soldier of Silence and bringer of revolution.

Saturn is arguably the most powerful of the senshi, with the power to destroy the toughest foe and even entire worlds with a simple swing of her Glaive, a large sythe-like weapon she carries around with her. This power is a double edged sword however, and the use of the Power of Death which she wields also results in her own life ending. She is the leader of the Outer Senshi.

Hotaru is the daughter of Souichi Tomoe, a reknown professor who, several years ago, sold himself to an entity called Mistress Nine in return for saving the life of Hotaru after a lab experiment. The result of this was Mistress Nine occupying Hotaru's body in a state of dormancy as the Sovereign of Silence, until the Professor could find the purity chalice (formed when the 3 heart crystals of the purest hearts are combined), which had the power to awaken the Sovereign and open a portal to the Tau Nebula, where an all-powerful entity known as Pharaoh 90 existed, the result being Pharaoh 90 coming to Earth and bringing about the end of the world.

Partly due to having 2 people living in her body, Hotaru was physically weak, and prone to fainting and taking ill. She is an only child and has few friends, as others tended to become afraid of her special abilities she's had since childhood, such as healing wounds by touch. This did not stop her befriending Chibiusa, however, and they have been very close since.

At the end of the S series, Hotaru finally awoke as Sailor Saturn and defeated Mistress Nine and used the Power of Death to defeat Pharaoh 90, but was saved from death herself by Sailor Moon, who returned with her as a baby. She was then returned to her healed father, where she lived until the Stars series, when she was awoken again by Galaxia and grew back to the age she was previously in the space of a few days.

Hotaru is a very shy and frail individual, who cares for others and apprciates sincere friendship. She lives with her father, Professor Tomoe, and for a short time Kaorinite also.