The Oni are hideous horned demons who, in Japanese fairy tales, are rumored to eat the souls of naughty children. Oni are repelled by onions which cause them temporary blindness and severe eye irritation.
In ancient times, Tarakudo, lord of all Oni and king of the Shadowkhan, along with his nine demon generals, terrorized Japan. Ancient Chi warriors carved masks and, through use of good Chi spell ingredients, trapped the Nine Generals in those masks. One was made for Tarakudo who found the mask and hid it in the Shadow Realm. His whereabouts were unknown afterwards. The masks were then scattered across the Earth. If united the nine Oni generals would be released and summon an army of Shadowkhan to engulf the Earth in eternal darkness which will cause all good magics to erode.
The masks summon Shadowkhan when they are attached to a host (any species of animal). If worn too long the masks will possess the wearer until he/she is consumed by the demon's psyche. Each mask has a different tribe of Shadowkhan and a different removal ingredient.
Each Oni greatly resembles the Shadowkhan he summons. The only exceptions to this rule are the Shadow-Eater Khan and the Mantis Khan.
A favorite Oni Catchphrase is " I shall devour your brains " as seen with Ikazuki and Jade when wearing half of the black mask
At an unknown point in time, Shendu found the maroon mask and a means to tap its power indirectly, letting him summon ninja Shadowkhan without wearing it. He kept it in a chest in his palace until it was found by Tarakudo and the Enforcers. This same mask's powers were later briefly accessed by Jade and Daolon Wong on separate occasions.
Ultimately, all ten Oni were sealed away within Tarakudo's mask.
The Oni Masks consist of:
|Image||Color||Worn by||Summons||Mask removal ingredient|
|Maroon||Chow||Ninja Shadowkhan||Japanese steel|
|Purple||Ratso||Razor Shadowkhan||Japanese silk|
|Yellow||Scruffy||Bat Shadowkhan||Japanese rice|
|Green||Captain Black||Sumo Shadowkhan||rare Japanese seaweed|
|Blue||Finn's butt||Samurai Shadowkhan||Japanese armor|
|Orange||Paco||Squid Shadowkhan||Tentacle of Japanese octopus|
|Yellow-green||Hak Foo||Mini/Leech/Shadow Eater Shadowkhan||Japanese fish|
|Black||Valmont (right half) and Jade (left half)||Crab Shadowkhan||Tears of Japanese monkey|
|Red||Nobody||Mantis Shadowkhan||Japanese leaves|
|Tarakudo||Tarakudo (to seal him)||Unknown; possibly all of them.||Hair of Japanese Samurai|