The Death Busters are the main antagonists of the fourth arc of the Sailor Moon manga and anime.
Hailing from the Tau Nebula, outside the solar system, the ultimate goal of the Death Busters is to usher their master, Pharaoh 90, to Earth in order transform it into a silent wasteland. To accomplish their goal, they require an object known as the Holy Grail. To aquire it they need to find three talismans hidden in the Pure Heart Crystals of humans.
Several years prior, the Daimon Germatoid possessed the body of Doctor Tomoe, a leading geneticist, after a lab accident injured him. His daughter Hotaru, who was near death from the same accident, was implanted with a being known as Mistress 9, saving her life. Following all this, Doctor Tomoe established the Mugen Academy as a secret base for the Death Busters.
Tomoe and his assistant, Kaorinite, began using Daimons to extract the Pure Heart Crystals of people in order to find three talismans hidden among them. Their actions soon drew the attention of the Sailor Guardians, especially Sailors Uranus and Neptune.
After several attempts at finding the talismans, Kaorinite was killed in a fight with the Sailor Guardians. With Kaorinite gone, Tomoe turned to Eugeal, the chief operator of Witches 5, to find the talismans. She eventually discovered the locations of two talismans, hidden in the hearts of Sailors Uranus and Neptune. When Sailor Pluto appeared with the third talisman, the Holy Grail appeared. Though she tried to claim it, Eugeal was beaten by Sailor Moon. During her getaway, Eugeal found her van had been sabotaged by her rival, Mimet, causing her to crash into the sea, killing her.
With the Holy Grail found, Mistress 9, who had been dormant inside of Hotaru, finally awakens. However, she required the energy of Pure Heart Crystals to fully regain her powers. To that end, Mimet was tasked with using new Daimons to extract Pure Hearts. After being foiled by the Sailor Guardians several times, Mimet fell out of favor with Doctor Tomoe, and was to be replaced with Telulu.