Yōkai (kanji: 妖怪, "strange apparition") are a class of supernatural or paranormal beings in Japanese culture, myth, and religions. A synonym for yōkai is mononoke (Japanese: 物の怪).
Species and groupings of yōkai are massively diverse, and range from beasts to demons to spirits, while their motives, appearances, and abilities are just as diverse. Ayakashi (hiragana: あやかし) is an umbrella term for yōkai that manifest above the water's surface, like the ikuchi. Henge (kanji: 変化) is an umbrella term for yōkai that shapeshift into other forms, like the tanuki.
In TMNT[]
Since many of the characters in the Teenage Mutant Ninja Turtles franchise are from and/or visit Japan, yōkai are featured occasionally in various incarnations. The Ninja Turtles themselves are mistaken for kappa in multiple incarnations, usually by the people of feudal Japan.
TMNT Adventures[]
In the Teenage Mutant Ninja Turtles Adventures comics, Umihaha may be based on the ikuchi, given her Japanese name and status as a sea serpent.
2003 TV series[]
In the 2003 TV series, "Tengu" is a catch-all term for Japanese demons/yōkai. Among the tengu mentioned are Ultimate Ninja and his father, the original Shredder and his possession of Oroku Saki, the Kappa Tengu (which are kappa), and the rat-like Nezumi-Tengu. Baku is modeled after the original, chimeric creature from Japanese myth of that name.
IDW[]
In the IDW contiunity, "Kitsune" is the Japanese word for "fox". Foxes were considered yōkai and were portrayed as magical tricksters. Ocho is noted to be a mole yōkai and a former human. Like "Kitsune" and "tanuki", "Namazu" is just the Japanese word for a common animal ("catfish", in this case), but they were given yōkai status and powers through myth. Namazu in myth, like here, created earthquakes.
2012 TV series[]
In the 2012 TV series, Joroguma is based on jorōgumo, half-woman, half-spider creatures capable of disguising themselves as beautiful women. While tanuki are a non-fictional animal species, the Japanese raccoon dog, there were myths surrounding them regarding their motivations, personality anthropomorphism, and powers, which are displayed here.
2012 video games[]
Several of the Power Rangers villains that appear in Power Rangers vs Teenage Mutant Ninja Turtles: Ultimate Hero Clash 2 are based on yōkai: Cat O'Clock is a nekomata, Ripperat is a kamaitachi, Skullgators are alligator gashadokuro, and Stonedozer is a construction equipment-themed daidarabotchi.
2014 film series[]
In the 2014 film series, the Kappa Yokai are a team of four kappa who saved ancient Japan, and are a spiritual predecessor to the Ninja Turtles.
Rise of the TMNT[]
In Rise of the Teenage Mutant Ninja Turtles, Yōkai are featured quite prominently, residing in a society called the Hidden City below ground in secrecy from humanity. Yōkai have a special common origin, having been mutated in ancient times by the Krang's Empyrean.