Ancient demons of thunder and fire, the Oni are famous for being in Japanese folk lore for their strength and drinking capabilities. They appear many times in the Ultra series, their first debut being in 1972's Ultraman Ace.
Oni are usually supernatural, sentient monsters, usually originating from Earth. However, there are some space creatures, mainly aliens, who bear many similarities to this archetype and therefore fall under this category.
- Japan's most famous Oni, Invader Lum of Urusei Yatsura fame, makes multiple connections to the Ultraman series, via cameos, mention of aliens, and even cosplaying as monsters.
- In one incident involving the western zodiac and fortunetelling, Gemini was represented by a pair of Ultras who even fired beams.
- In another instance, in one of the main character's imagination, a possible mother-in-law was represented as have a head similar to Mother of Ultra's