The goal of the Death Busters is the resurrection of Mistress 9 in order to bring the alien creature Pharaoh 90 to Earth, which would wipe out all life in an event known as the Silence. The group is led by Professor Tomoe, a mad scientist, assisted by a woman named Kaolinite. They employ the Witches 5 to help carry out their schemes.
In the anime, creatures called Daimons serve as monsters-of-the-day. These life forms are bred in special pods that release monsters from the most mundane of objects, and are employed by Kaolinite and the Witches 5. They hunt down Pure Heart Crystals, which may contain the mystical Talismans, or may simply be used to give power to Mistress 9.
In the manga Tomoe is outright malevolent. It is learned that he was rejected by the scientific community for his genetic experiments on animals and eventually sold his skills to the highest bidder: the Infinity Academy of which he is now headmaster He joins the Death Busters of his own free will after a lab fire that killed his older wife, Keiko and seriously wounded his young daughter Hotaru Tomoe. He continues his experiments at the Infinity Academy, attempting to create superhuman beings by combining humans with foreign elements. The sluglike daimons used by the Death Busters are his failed creations and he hints that the Witches 5 are results of his more successful work. He later turns himself into Germatoid (the pinnacle of his experiments) to fight Sailor Moon but is killed after being hit by Sailor Moon's Rainbow Moon Heartache. He dies in the manga and does not come back.
In the anime he is a more sympathetic character. He displays bizarre, but hilariously overdramatic mannerisms, which are often a source of unexpected humor. It is never specified whether these are mannerisms of Germatoid or repressed aspects of his personality, since little is known of him before or after the possession. His normal personality does show through at times, however, revealing him to be a kind and loving father. At the end of S, he is shown wheelchair-bound in a hospital with no memory of any of his Death Buster activities, his amnesia being a symbolic rebirth. He has taken it upon himself to re-raise the now infant Hotaru.
Professor Tomoe makes one more appearance in the anime, namely in episode 167 (the first episode of the Sailor Stars season), when Sailor Pluto arrives to take baby Hotaru from him. In this episode, his last appearance in the series, he is seen without his glasses and no longer relies on a wheelchair, indicating that his condition is improving.
A difference between two variations is Kaolinite's treatment of Hotaru: while in the anime Kaori frequently provokes and mocks Hotaru, in the manga she shows concern towards the girl. Hotaru, however, feels that Kaori's presence in the family home is a sign that she does not know her place.
Kaolinite demonstrates several powers throughout the series, including levitation, teleportation, limited shape-shifting, and using her hair as a weapon (similar to Mistress 9). She also appears in the stage musicals.
Kaolinite's role in the original manga is slightly different. As opposed to the anime, where her origins are unknown, it is revealed in one of Professor Tomoe's flashbacks that she became Kaolinite after being struck by random lightning during a chaotic storm that occurred as the pair attempted to reconstruct the maimed body of his daughter Hotaru. When she rises from the floor, her eyes are shining. Her title is "Magus Kaolinite", Magus being a position that all of the Witches 5 aspire to reach. The privileges of the Magus position includes the use of the Tau Star System's crystal and direct contact with Master Pharaoh 90.
In the manga, it is Kaolinite, not Tomoe, to whom the Witches 5 answer. She sees them in no way other than servants, demonstrating annoyance when Mimete appeals to her for help. It is implied that she wishes to be Pharaoh 90's partner in place of Mistress 9, something Mistress 9 is aware of and views with amusement. When Mistress 9 does awaken, she orders Kaolinite to eliminate the Sailor Senshi. She succeeds in subduing the Guardian Senshi, they are freed by Uranus, Neptune, and Pluto. Reunited, the Senshi confront Kaolinite in the President's office of Infinty Academy, and she transforms into a Daimon. Ultimately, she is destroyed by Super Sailor Moon's "Rainbow Moon Heartache" attack.
In the Japanese anime, she is portrayed by Noriko Uemura, who also voiced Queen Metaria in the first story arc. In the English dub, she is voiced by Kirsten Bishop, who was also the voice of Zoycite, Emerald, and Badiyanu.
In the anime, she is the first of the Death Busters to openly attack people who possess pure heart crystals, using the bio-engineered Daimons she helped create. Her goal is to find the three Talismans, which (unbeknownst to her) are possessed by Sailors Uranus, Neptune, and Pluto. The Daimons she sent after others were created by merging pods with inanimate objects. They were then brought forth when the intended target touched that object. The Daimons would then extract the Heart Crystals by casting a black beam from a black star (the Death Buster's symbol) somewhere on their body towards its target's own heart (which was usually accomplished, after the target was immobilized). Sailor Mars, Sailor Mercury, and Sailor Jupiter were all targeted by her monsters. In episode 102, she discovers the brightness of Sailor Moon's Pure Heart Crystal and goes after it. The Sailor Senshi rally against her, and she is subsequently defeated by Sailor Uranus, whose "World Shaking" attack causes a glass related attack she was using against the Senshi to feedback on her, encasing her in a pillar of glass and causing her to fall from the Tokyo Tower.
In episode 113, she suddenly reappears as Hotaru Tomoe's guardian, calling herself Kaori (except in the dub, where she is still Kaorinite). It is later revealed that Professor Tomoe himself had managed to revive her. However, she feels that her place has mostly been filled by the Witches 5, and is jealous of them as well as Hotaru. By episode 123 she is filled with hate, and steals the Pure Heart of Sailor Chibi Moon, Hotaru's best friend. The crystal is ingested by Hotaru's possessed form, and she awakens as Mistress 9, the "Messiah of Silence." The last words Kaolinite hears are congratulations from Professor Tomoe, before she is thrown into an electrified wall by Mistress 9 for "having served her purpose."
In the manga, the Death Busters are frequently striving to awaken Mistress 9. When the Death Busters first visited Professor Tomoe (as he was reconstructing his daughter Hotaru's body), one of the objects they gave him was an egg that contained Mistress 9. He implanted it within Hotaru's body. The consequence of this for Hotaru is a permanently frail physical state. She occasionally suffers from seizures that are soothed at first by an amulet given to her by Tomoe (he tells her it is an heirloom, but it is more likely to be a fragment of the Tau Crystal) and later by the Ginzuishou. When Chibiusa shows it to Hotaru, Mistress 9 becomes aware of it and later grabs it from Chibiusa, sending her into a coma.
When Mistress 9 overpowers Hotaru's body, it becomes that of a grown woman. Her facial features are maniacal and there is little resemblance to the girl whose body she has taken over. Her purpose is to create an opening to the Tau Ceti Star System so that Pharaoh 90 can access and assimilate himself into Earth.
Once all of her allies have been killed and she is confronted by Sailor Moon and the Outer Senshi, her plan begins. Mugen Gakuen itself is ripped apart, throwing the unconscious bodies of Mercury, Mars, Venus and Jupiter into the air (they come to rest on a structure that Kaolinite previously used for divination). She then attempts to escape Hotaru's body (meaning that her power will be able to flow freely) but is surprised to find that the soul of Hotaru still exists within the body and is inhibiting her from leaving it. Nonetheless she swallows the souls of the Guardian Senshi whereupon Hotaru retrieves their Heart Crystals along with that of Chibiusa and escapes to return them to their owners. While she is doing this, Mistress 9 is able to leave Hotaru's body, ripping it apart in the process. Her true form is of a gigantic monster with ghoulish head and an indistinct body.
She absorbs all of the Senshi's attacks and opens the door for Pharaoh 90, who begins to smother the planet. Mistress 9 is assimilated into the lava (which presumably is Pharaoh 90) and just when all seems lost, Sailor Saturn rises from it. When she sets her Glaive into the ground, both Pharaoh 90 and Mistress 9 experience intense pain and paralysis. Saturn uses the attack Death Reborn Revolution to drain their power and they both rise into the sky to escape back to Tau. Saturn follows them and commands Sailor Pluto to seal the door forever. Pluto does this and assures that Mistress 9 and Pharaoh 90 can never reach Earth again. Interestingly enough, they are the only villains in the Sailor Moon manga to not only evade death, but essentially remain unharmed.
In the anime, Professor Tomoe allows Mistress 9 to possess Hotaru's body after a freak accident kills her. He himself becomes possessed by a Daimon named Germatoid, although it is unclear if Germatoid completely controls him or aspects of his original personality still exist. Mistress 9 occasionally controls Hotaru, sequences in which her eyes become blank and her hands sparkle with red energy. Strangely enough, the victims of these occurrences are usually Daimons sent to collect heart crystals for her. Eventually, she steals Chibiusa's Heart Crystal, rendering Chibiusa close to death, she becomes Mistress 9 to the shock of Uranus and Neptune, who are expecting Sailor Saturn.
She kills the underling Kaolinite, and sends Germatoid after the Senshi. She then attempts to use a large machine (similar to the one Tomoe created prior to possession) to guide Pharaoh 90 to Earth so that he may destroy it. Sailor Moon tries to stop her and Professor Tomoe, now freed from Germatoid, attempts to reach her, still seeing her as Hotaru. She attacks both of them but is injured by energy emanating from the machine. Professor Tomoe takes her in his arms and Hotaru's spirit begins to respond. Mistress 9 attempts to subdue her once again but Hotaru's memories of both her father and of Chibiusa prove to be overpowering. The black star insignia on her forehead shatters, revealing the sign of Saturn beneath it. Mistress 9's body then vaporizes, leaving Saturn in its place.
Whilst in the manga Mistress 9's human form seemed only to be Hotaru's body contorted due to the presence of the entity, the anime Mistress 9's form seems to be her genuine body, somewhat similar to Chibiusa's transformation into Black Lady.
In the original anime, Mistress 9's voice is provided by Yuko Minaguchi. In the English dub, she is played by Jennifer Gould. In the musicals two actresses have played her: Tomoko Inami and Chinatsu Akiyama.
In the manga, Pharaoh 90's goal is to merge itself with the planet Earth and make it his home. Throughout the manga, this process is referred to as "the utilization". To do this, it requires Mistress 9 to open the gateway between the Tau System and Earth. Its role in the manga is more prevalent and it communicates regularly with Kaolinite and Tomoe through a reflecting pool concealed at the top of the Infinity Academy, reminding them of the importance of their mission. When it first appears, it is dependant on the Taioron Crystal, the life source of the Tau System. The Crystal is losing its power, presumably due to Pharaoh 90's presence but it identifies a replacement in the Silver Crystal.
Mistress 9 is able to open the gateway and Pharaoh 90 begins to cover the Earth; Sailor Moon describes its form as that of black lava reeking of death It is energized by the attacks the individual senshi use on it and in a last ditch attempt, Sailor Moon throws herself into its mass with the Legendary Holy Chalice and the Silver Crystal with the intent of unleashing the full power of both while inside of it. Her manoeuvre seems to cause a reaction in the three Talismans of the Outer Senshi and they summon Sailor Saturn. Saturn's "Death Reborn Revolution" drains Pharaoh 90's energy and it attempts to escape back to the Tau System, along with Mistress 9. Sailor Pluto then uses Dark Dome Close to seal the gateway, permanently locking Pharaoh 90 away from Earth. Like all of the head villains in the manga, Pharaoh 90 is later revealed to be an incarnation of Chaos, the ultimate enemy of the series.
In the anime, it wants simply to destroy it by bringing about the Silence. Pharaoh 90 is the one who provided the daimon egg of Mistress 9 to Professor Tomoe, taking advantage of Tomoe's desire to save his daughter. In reality, Pharaoh 90 simply needed to provide a body for Mistress 9 so that she, in turn, could open a portal for Pharaoh 90. When the portal is opened, it appears on Earth but Sailor Moon using energy from the other senshi and the newly awakened Sailor Saturn defeat it.