Reugosite

Reugosite (ルーゴサイト) is the final villain of Ultraman R/B. It is stated to be a dreadful life form that brings catastrophe to the universe.

Subtitle: Cosmo Eater (コスモイーター)

Pre-Ultraman R/B
Reugosite was a planet-eating monster that destroyed everything in its path. 1,300 years ago, It came across Earth and was met with resistance in the form of three warriors sent from Planet O-50; Ultraman Rosso, Ultraman Blu and Grigio Bone, the latter being transformed into by Saki Mitsurugi. Reugosite attempted to destroy them and managed to knock them onto Earth, resulting in the Ayaka Comet incident. After that, Reugosite seemingly left.

Ultraman R/B
As Aizen Tech detected that Reugosite would be returning to Earth, Saki plans to turn the planet into a massive bomb in an attempt to destroy the powerful monster. Having returned to Earth during the present times, Mio's plan suceeded in sealing Reugosite into an R/B crystal with the three Gyros. However, Saki claimed the crystal after Mio attempted in trapping it into the dimension she disappeared previously, stating its not the solution in stopping the latter. After Saki defeats Ultraman Ruebe as Grigio Regina, Reugosite's R/B Crystal activates itself, cancelling out her transformation and assuming his true form via Saki's Gyro.

Trivia

 * Reugosite's concept art from the toy catalog has been widely compared to Greeza by fans.
 * Its name is one kana away from the Japanese transliteration of Leukocyte (ルーコサイト), the technical term for white blood cells. Mio Minato also makes this allusion, saying that Reugosite is like the white blood cell of space that has determined that Earth is like a virus that should be annihilated.