First appearing in SailormoonS, many immediately fell in love with the frail looking schoolgirl who always seemed to be sick. However, Little did we know, this frail looking school girl was the Dark Messiah, the Silent Senshi.
Hotaru is a loner, most of the kids in her school avoid her because of her unusually sickly appearance and "gross" healing ability. Hotaru soon became friends with Chibi-usa, who sees Hotaru and befriends her when she retrieves Chibi-usa's lost hat. Later on that day, a daimon appears. Chibi-usa wanted to transform, but couldn't because Hotaru was there. They hid in the bushes. Unfortunately, the daimon spotted them and started after them. Chibi-usa pushed Hotaru out of the way. The daimon caught Chibi-usa. There was a short battle between the daimon, Sailormoon and Sailorpluto. When this was over, Chibi-usa went back to Hotaru and collapsed. She was injured, so Hotaru healed her. Hotaru explained how kids at school thought the healing to be gross, however, Chibi-usa felt it was a great ability. Since then, the two of them were great friends. (See Bells for Her for more info)
Hotaru collects lamps. When Chibi-usa first went to her mansion, she was amazed at the many beautiful lamps that Hotaru owned. Hotaru aspires to be a doctor. She was born on January 6th, so her astrological sign is capricorn. Her hobbies are collecting the lamps which made Chibi-usa so awestruck and reading. Her favourite food is nihon soba and her least favourite is milk. Her best subject is world history, her worst subject is physical education because of her weakened health.
Hotaru's mother died when she was young so she lives with her father, Professor Tomoe Souichi. He was possessed by a daimon and collected heart crystals to summon Pharoah Ninety. In the meantime, Hotaru was weakening. The evil inside her, Mistress Nine, was strengthening and possessing the young Hotaru's (16 years old) body. Hotaru weakens throughout Sailormoon S to the point where her father's assistant, Kaolinite, steals Chibi-usa's heart crystal to give it to Hotaru for energy. Chibi-usa's purest heart crystal makes Hotaru transform into Mistress Nine, the Dark Messiah. Mistress Nine is an older version of Hotaru and is the only one besides Sailormoon who can control the Holy Grail. Her hair is rumoured to be infinitely long. She uses it as a weapon, to squeeze the life out of anyone she chooses. Neptune and Uranus attacked Tomoe. A daimon sprung from him. They destroyed it. Tomoe was back to his original state, not evil. Mistress Nine tricked Tomoe to get the holy grail by using Hotaru's voice. When Mistress Nine obtained the Grail, she summoned Pharoah Ninety. The nuclear winter, the silence had begun. Meanwhile, inside of Mistress Nine, Hotaru was struggling to free herself from this evil. She is overwhelmed with memories and regains control of her body. She proceeds to transform into Sailorsaturn.
As Sailorsaturn, Hotaru is full of energy, calm and rather frightening. Especially when she's pointing her sythe-like glaive in your face. Yes. The silence glaive. It slices, it dices, it blows up devices– and even whole planets with the simple saying of three words: Death Reborn Revolution. Sailorsaturn, although evil when Mistress Nine, uses this attack to destroy Pharoah Ninety.
The next time we see Hotaru is when she is a baby. It is in the first episode of SMSS. We see her in a crib. Baby Hotaru has a vision of Eternal Sailormoon. Pluto takes Hotaru in this dream from Sailormoon. Later on in this episode, Pluto reappears with the little firefly. She places her down in a flowerbed while she and the other Outer Senshi attack a mirror paredory. The outer senshi were threatened by these mirror fragments. While they were being held back, one went after Baby Hotaru. This was a mistake. Baby Hotaru's gaze made them explode. A Saturn symbol appeared on her forehead. The outer senshi combine powers to completely destroy the mirror paredory. They wonder if it's a new evil and hear a voice behind them. They turn and see Hotaru grown to four years of age. Hotaru rapidly grows both physically and spiritually. One night, Hotaru is confronted by the spirit of Sailorsaturn. Sailorsaturn touches Hotaru's forehead with a ball of light. This makes Hotaru remember what happened in SailormoonS. The Saturn symbol once again appears on her forehead. She later appears as a girl of 16 again.
Sailorsaturn has three more appearances in the Anime Series. These appearances are when she battles Neherenia, when she dies at the hand of Galaxia, Neptune and Uranus and when she appears in the final episode.
The battle with Neherenia was astonishing. She demonstrates true power in this battle, using Silence Wall and Silence Glaive Surprise! Neherenia attacks Mamoru, who is possessed. This is where Saturn blocks it with Silence Wall. She steps forward and holds her glaive up. She and Neherenia argue. Then Neherenia attacks her again, Saturn resists. Saturn raises her glaive and uses a margin of its energy in a Silence Glaive Surprise. This destoys a lot of the castle and makes a huge hole in the floor. Neherenia distracts Saturn after this, knocks her glaive away and traps her in a mirror.
In episode 197, we learn something startling about Saturn. We learn that Sailor Galaxia is the one who brought Hotaru back to life after she was destroyed when defeating Pharoah Ninety. When she brought back Neherenia, she brought back Hotaru as well because she needed all the star seeds. Neptune and Uranus offer their starseeds in exchange for bracelets and loyalty to Galaxia to stay alive. They are ordered to take Saturn and Pluto's starseeds. Rather than fighting against their friends, they allow themselves to be destroyed. We see Hotaru's loyalty to Sailormoon and the cause of good.
Finally, in episode 200, we see a happy ending, as we do with most fairy tales. All the senshi, after dying, are brought back to life. The final scene before the Usagi/Mamoru love/kiss scene. We see the outer senshi in a car talking. They see a shooting star and make a wish. It is a wonderful ending.