Real Name: Tomoe Hotaru
|Hotaru is...well, she was
a kind, caring, shy girl. She has the power to heal people by just
touching them. In school, the kids bullied her and thought she was
strange because of her healing powers, so she had no friends. Until
she met Chibiusa, that is. Chibiusa was in the park and the wind
blew her hat away, so Hotaru went to get it. She was exhausted from
the excercise and nearly fainted, but she didn't mind since she had done
it to help Chibiusa (whom she didn't even know at the time). Chibiusa
had gotten a cut on her knee, and Hotaru healed it for her. Chibiusa
thought Hotaru's healing power was great and became her friend, probably
Hotaru's first, only friend so far in her life. After that she started
doing things with Chibiusa and the senshi, who really liked her and cared
for her and wanted to protect her.
But Hotaru had a very disturbed past. Her mother died when she was young and she and her father almost died themselves. There was an explosion in her father's lab, and Hotaru was killed. But Master Pharaoh 90 (the bad entity thing of SMS) appeared to Tomoe Souichi and offered to revive Hotaru if Souichi would do him (it?) a favor. Souichi said he'd do anything if Hotaru could live again, but little did he know that Pharaoh 90 would possess him and Hotaru too. Pharaoh 90 is from the Tau Ceti star system, and he aims to silence the world (basically, he wants to destroy it). Hotaru was possessed by Mistress 9, almost like she had split personalities (an evil side, and a good side). Pharaoh 90 planned for Hotaru/Mistress 9 to silence the world. She's also known, in her Mistress 9 form, as the Messiah of Silence (as opposed to Usagi, who is the "good" Messiah).
The Outer Senshi (the other ones, excluding Saturn) realize that Hotaru is the Messiah of Silence when the sign of Saturn appears on her forehead. When they find this it's almost like they don't think of Hotaru as a real person anymore, but just as this evil thing that needs to be killed. And they do try to kill her, but either she blocks their attacks or Usagi stops them from doing so and saves Hotaru.
But then Hotaru swallows Chibiusa's heart crystal, and this allows her to turn into Mistress 9. She would probably have been totally possessed by Mistress 9, but Souichi's love for Hotaru and Chibiusa's friendship with her gave her the will to live, and she tried to escape from Mistress 9. But Mistress 9 tricked Usagi into giving her the Holy Grail (stupid baka Usagi!), and she was about to silence the world, but then Sailor Saturn's spirit came out of her, returned Chibiusa's heart crystal, and was going to do Death Reborn Revolution on Pharaoh 90. But Usagi didn't want her to do this because Hotaru would be killed in the process, so Usagi summons all the senshi's power and kicks Pharaoh 90's butt on her own.
Hotaru is then reborn as an infant, possibly because she used up so much of her power it reverted her to a child. In the anime, she goes off to live with her father again after this happens and the Outer Senshi go on a trip around the world (which is why they're not in the SuperS anime). The manga is a bit sadder, however: Hotaru loses her memories, Souichi dies, and the Outers adopt her. She eventually does turn back into Sailor Saturn, and she gives the Outers their power-ups into Super form.
So basically, Hotaru doesn't have a really complex personality on her own (she's quiet, kind, and smart, like Mercury), but as Mistress 9 she's more schizophrenic, split-personalities type. She's insane as Mistress 9; Mistress 9 kind of gives her more personality. But she has a fascinating history, even moreso in the manga than in the anime. I think of her as a half-evil Mercury, only lots cooler.
Silence Glaive Surprise
Death Reborn Revolution