Oo-ze is an extraterrestrial parasitic organism whose nutrient source is calcium carbonate. It arrived on Earth by parasitizing space kaiju, shifting hosts to continue its consumption. There have been four reported cases of Oo-ze appearances abroad (the United States, Germany, Chile, and China). In Japan, Oo-ze lay dormant for 16 years within the horn of Monogelos (known as the "Monohorn") located at Mt. Shishio in Hoshimoto City. Once revived, Oo-ze burst through the horn's surface and then shifted its host to Shagong. As a result of the parasitism, Shagong underwent a drastic change from carnivorous habits to consuming stalactites. Influenced by the hormones secreted by Oo-ze and the abundant new food source, Shagong experienced rapid growth, reaching a size of 50 meters.

The mother of Oo-ze that parasitized Shagong proliferated multiple offspring. When Shagong was attacked by the GDF, these offspring crawled out of the crevices in Shagong's shell and attacked factory workers. Yuma tried to deal with them using SKIP's supersonic intimidation device, the Soniter; although the Oo-ze briefly recoiled at the flash emitted by the Soniter, the effect was minimal, thus Shu had to help using the Elemagun. When Shagong was defeated by Ultraman Arc, Mother Oo-ze emerged from the explosion, growing into a giant form to attack Ultraman Arc.