En no Ozuno (役小角?, エンノオズノ?, or エンノオヅヌ?) is a demon in the series.
Also called En-no-Gyoja (or En-no-ozunu), he was born in Yamato no Kuni (present Nara prefecture) in the era of the emperor Jomei. He was wise in his childhood, pursued for classical books, through knowledge of the doctrine and mastered Sanpou (the law of Buddha, the laws, the priest). Later, he practiced ascetic training in Mt. Ikoma in Yamato (present Nara) and, in Mt. Kumano in Kii(present Wakayama prefecture), he climbed Mt. Katruragi and enshrined Kujaku Myoo and practiced ascetic training, which made him manifested. He was accused of entirely contrary to the fact, he was sent to Izu. He came back to Kyoto after being released and became a founder of Shugen-do (mountaineering ascetism). Later he was manifested in Buzen Kyushuu (present Ooita). He could not be traced then after. His servants are called Zenki and Goki. He was deigned the title of Shinpen Daibosatsu in 1799.
After Thor barrages Japan with ICBMs, the heroine sends the protagonist to the Diamond Realm where he meets En no Ozuno. He asks the player to fetch him some Soma twice, and then locate Blue Phantom and Red Phantom (they will fight if the protagonist's alignment does not match either of theirs) to gain alignment-exclusive weapons (the Light Sword for Law and the Headsman Ax for Chaos). Afterwards, he sends them back to Tokyo 30 years later, but not before fighting his servants, Zenki and Goki.
Shin Megami Tensei II
En no Ozuno appears again in the Diamond Realm, which area is unlocked by completing the game once (There must be a second file saved before going to Eden, in order for the area to appear).
Devil Children Black Book/Red Book (PS)
En no Ozuno is a level 34 Battle Net opponent. He mostly uses Tengu demons and gives Zenki Goki after being defeated.