Zaou-Gongen is one of the most important mountain deities of Japan's syncretic Shugendou sects, a diverse tradition of mountain ascetic practices associated with Shinto beliefs, Taoism, magic, supernatural powers, and Esoteric (Tantric) Buddhism. After the arrival of Buddhism to Japan in the mid-6th century, the native Shinto Kami were soon considered manifestations of the imported Buddhist divinities. Zao serves as the protector deity of sacred Mt. Kimpusen Japan's Nara prefecture and is considered the local Japanese Shinto manifestation of three Buddhist divinities -- the Historical Buddha (Sakya), Kannon Bodhisattva (Kanzeon), and Miroku Buddha (Maitreya), who serve respectively as the Buddhas of the Past, Present, and Future. This makes Zaou perhaps the most powerful local divinity of religious mountain worship in Japan.
Zaou is widely venerated in the entire mountain range stretching from Yoshino to Kumano (the cradle of Shugendou practice), but also venerated at numerous remote mountain shrines and temples throughout the country. Despite Zaou's Tantric appearance, the deity is generally thought to be of Japanese origin. Zaou's cult spread throughout Japan from the 11th century onward. He is also called Vajragarbha.
Zao Gongen appears in some cultural content of Japan, mostly classical, such as Kuze Noh, where the gods protect Emperor Temmu, 40th Emperor of Japan, against enemy soldiers pursuing him.
"Repeller of the evil found by En-no-Ozunu at Kinpussen. He perceived the god when training for 1000 days looking for power to save the chaotic world. Buddha, Guanin, and Maitreya appeared before, but it was only when Zaou-Gongen appeared that Ozunu accepted him, believing this god could save the world."
In episode 12, the seventh day, Zaou-Gongen is summoned alongside Nebiros by Yamato Hotsuin in deep grief of Makoto Sako's sacrifice in order to protect the former from Alcor's deadly attack. After Yamato has survived Alcor's self-destruct attack, he uses both demons to block the path of Hibiki Kuze, Daichi Shijima and Io Nitta to buy him time to ascend to Polaris' throne. Zaou-Gongen is engulfed by the void. In the final episode, Yamato fuses Zaou-Gongen and Nebiros together to produce Satan.