Master Pharaoh 90, a cosmic entity from the Tau Star System's Tau Nebula, spearheads the Death Busters' invasion of Earth as their primary antagonist. Initially appearing as an amorphous shadow with glowing eyes, he later manifests a liquid-like form enveloping Earth after merging with Mistress 9 and the planet, developing distinct red pupils. His dimension deteriorated due to the weakening Taioron Crystal, his power source, prompting his quest for a new world. Sensing Sailor Moon's Silver Crystal on Earth as a potential replacement, he exploited Professor Souichi Tomoe's gene-splicing experiments. A lab explosion killed all except Tomoe and his daughter Hotaru; Pharaoh 90 offered their salvation in exchange for possessing their bodies. Tomoe accepted to ensure Hotaru's survival. Commanding the Death Busters through Kaolinite, Pharaoh 90 directed human soul collection to sustain the Taioron Crystal and prolong his existence. His ultimate goal was merging with Earth to create a "second mother planet" for his kind, annihilating all life. He relied on Mistress 9—implanted in Hotaru Tomoe—to gather energy and secure the Holy Grail or Silver Crystal, enabling his summoning and planetary assimilation. His powers included generating dark energy shields, creating Daimon eggs to possess humans, achieving colossal size, and channeling Tau Nebula energy. Linked to Mistress 9 and drawing nebular power, he spread his influence globally, corrupting Earth starting from the Omega Area around Mugen Academy after its barrier fell. During his planetary merger, Sailor Saturn awakened within Hotaru, binding and expelling him. Severely damaged, he retreated toward the Tau Nebula. Sailor Saturn pursued him, while Sailor Pluto sealed the Tau-Earth portal permanently using "Dark Dome Close," trapping Pharaoh 90 in his dimension. Later revelations identify him as an incarnation of Chaos, alongside entities like Queen Metalia and Death Phantom.