Rubeus was the first Black Moon Clan member to show up in 20th-century Tokyo, sent to hunt down someone codenamed "Rabbit"—Chibiusa, who'd escaped into the past. He answered to Prince Demand and Wiseman, though he also ran his own operation with a group of followers called the Ayakashi Sisters.
In the anime, Rubeus becomes the object of desire for most of his subordinates. Cooan, the youngest sister, is openly infatuated with him, and the others follow suit—except Petz, the eldest, who keeps her distance. After the Sisters are revived, Rubeus decides his best move is kidnapping the Sailor Senshi and forcing Sailor Moon into a hostage exchange: bring the Silver Crystal, get your friends back. Naturally, Sailor Moon shows up to fight for them. Rubeus hauls her and Chibiusa (who'd snuck along) onto his spaceship, where things quickly spiral. During the chaos onboard, Chibiusa finds and destroys the ship's control crystal. The vessel goes haywire, catches fire, and Sailor Moon's counterattack frees everyone. They teleport out just as the ship falls apart, leaving Rubeus behind.
Then Esmeraude arrives. She's not interested in saving him—he's failed too many times and his fixation on killing Chibiusa has made him useless. She leaves him to die in the explosion.
The manga version plays it differently. Rubeus manages to kidnap three of the four inner Sailor Senshi (Mars, Mercury, and Jupiter), though Venus gets away. He's intensely loyal to Prince Demand and appears alongside him to mock the captured Sailor Moon. But when Rubeus starts to realize Wiseman's true nature, he confronts him—a decision that costs him his life.
Content compiled by AnimeList.moe from publicly available sources.
