Appearance & Behavior
Small Oni are comprised of infected humans of varying sizes with little to no means of communication beyond guttural roars and yelps, with certain exceptions. The infection is caused by a non lethal wound of some sort, which later manifests itself as an excruciating transformation where the victim grows a horn or two somewhere on the head while the skin and eyes become discolored; the eyes are also engulfed by the now-yellow sclera (the whites in average humans). While certain victims with a strong will like Tatsuhito Saotome can temporarily resist the change, infection comes with a death sentence carried out by either completely destroying the body or destroying the cranium due to an Oni's regenerative properties that can oddly be stimulated by an electric surge in the correct places. While the Oni seem savage, they typically carry over their old memories to the point where they can handle piloting even the complex Prototype Getter Robo.
Larger Oni typically take on more imaginative and complex forms and are called forth by smaller Oni, but seem to show as much intelligence as their smaller "cousins". They initially have eyes similar to those of their smaller counterparts, but gain eyes closer to a human's after a larger Oni and a smaller Oni partake in an odd 'ritual' where energy flows from the horn of the smaller Oni to the larger one before the former human is devoured at which point the pupils and irises appear.
The exception for smaller Oni appear in the form of Abe no Seimei and his two 'handmaidens'; Seimei in particular. They show no horns and only have chalk-white skin as an indicator that they are not typical humans, physically speaking. Despite this, Seimei displays the ability to manipulate some type of energy as a barrier in a manner that resembles magic, and is durable enough to survive a Getter Ray-charged katana. When Seimei appears in the present, he appears bound along with his handmaidens to a larger type of Oni with his intelligence intact, and enough power to match Getter Robo with Hayato and Benkei piloting.
Of note is a statement by the leader of the Four Heavenly Kings faced at the end of New Getter Robo, that "The oni are the descendants of those eradicated by the Getter." While this statement explains their particular hatred for anything involving Getter Rays, it does not explain the Oni's infectious nature or how they came to be on Earth.
- The Oni are common antagonists from various series written by Ken Ishikawa alone including: Maku Hakkenden, Kyomu Senshi, Miroku, and Dogra.
- The various Oni seen throughout New Getter Robo are very similar to the villainous groups seen in the Getter Robo franchise up to that point.
- Small Oni stand in for the Reptiloids as well as the Oni from the Manga.
- Their infectious nature and lack of seeming reason reference both the Invaders as well as Dr. Lando's servants in the Getter Robo Go manga.
- This in turn was taken from the Oni of the Dogra series.
- Their origins as stated by the leader of the Four Heavenly Kings reference the Andromeda Country and the origins of Burai seen in the Shin Getter Robo manga.