History and Lore of Animegao Kigurumi
Animegao is a transliteration of the Japanese phrase アニメ顔, literally "anime face", it is not a term Japanese used to refer to Kigurumi yet it became to be one some westerners use to refer to Kigurumi masks. Lets explore how this term came to be.
It is not a term that is generally used in Japan, but does find rare usage in some contexts primarily in hashtags, SEO, or other outreach oriented contexts towards international audiences.
While the term has largely faded away in modern western contexts, it did previously find usage among some groups of kigurumi performers as an identity mark of sorts, but also as a unique SEO term some western makers reviled in to capitalize on the term for their own gain. Names need not be specified here, the makers who did so are largely of a bygone era and not intended to be vilanized over past actions, it is however worth a mention in the historical context.
Canonization via Wikipedia
The first known use of the term animegao was September 9th 2004 on Wikipedia, where an anonymous editor using a Japanese IP address made two notable series of edits.
Their first edit was to implement the term Kigurumi into the wikipedia page for Furry and mentioning the term Otherkin (アザーキン in Japanese) as a related term.
They quickly followed up with several edits to the page for Kigurumi, notably adding the first known usage of the term Animegao, in what seemed to be an attempt to distinguish Kigurumi masks from animal adjacent costumes.
Attempts at finding earlier usage of the term relating to Kigurumi have been fruitless, scraping the internet archive of any vintage Japanese kigurumi mask sites has not yielded any results either.
Furry and Kemono
Surprisingly lacking in the mystery Wikipedia user's additions and explanations is the notable term Kemono, the Japanese term for anthropomorphic animal related characters. A well researched primer on the history of Kemono can be found on Den-fami Nico Gamer with historical context provided by University of Tokyo researcher, Mr Tomohiro Inokuchi (猪口智広氏).
Notably, it denotes the rise of the term Kemono and its sibling term for fans of the genre, kemonā (ケモナー, sometimes also translated as kemoner) having both found common usage by the late 1990s. They do not describe it as Kigurumi, nor the western term "otherkin" (アザーキン) used by the Wikipedia user. Neither do they use otherkin to describe Kemono suiters in current or past versions of Japanese Wikipedia pages for Kigurumi, Kemono or Furry, and similar for Japanese Wikifur. Attempting to find any notable usage of the term in Japanese contexts in the 2000s remains similarly fruitless.
In person usage is difficult to find records of, especially as the first notable Kemono cosplay event Transfur was in 2005. We only have a 2007 web archive of their site these days, they preferred to use the term "kemono transformation" instead of using Kigurumi, otherkin, or likewise.
The Doll Connection
While the specific phrasing アニメ顔 (anime face) does not originate from the context of dolls, it was a term used at least by some in the early 2000s to denote the style difference compared to more realistic or traditional style dolls.
September 25, 2001 a very curious article on several "anime faced", human sized dolls.
December 1 2003 journals a doll fan's customized doll, notably designed after Gogo Yubari from the movie Kill Bill and using a Obitsu style doll head from Azone as it's base. While this doll itself is not anime styled, they describe having done a number of anime styled dolls in the past, using the term アニメ顔 (anime face) to describe their previous works.
March 18, 2002 notes a doll gathering event from earlier in the year.
June 30, 2002 shows various styles of Dolls, including many "anime faced" dolls.
While this is nowhere near a definitive or absolute list, it's usage with dolls is the closest historical context we have adjacent to Kigurumi masks.
Fun fact: The term Doller (ドラー) is another term that essentially means the same as a Kigurumi performer. This term was noted on the English version of Wikipedia even before Animegao Kigurumi was coined.
Early Notes of Anime Faced Outside Dolls
While there is some notable linking to it's usage with Dolls and how they relate to Kigurumi masks, it is worth noting the term was not exclusive to dolls.
You can find early uses of the term for other contexts, such as relating to Kaomoji in January 31, 2001, Kaomoji being a type of text-based emoji dating back to much earlier parts of the internet.
Around the same era you can also find usage denoting the use of anime styled characters in Video Games, for example relating to Metal Head or Might and Magic.
It goes to be said, the term is generically used to describe any character that is styled after an anime character, regardless of the medium.
Why does Wikipedia still use the term Animegao Kigurumi?
It is almost a greater mystery than the term itself. Wikipedia has a history of being resistant to changes, and this is no exception.
User and former Wikipedia Foundation member Zanimum is worth mentioning for both adding the term Doller to the page for Kigurumi, and being the initial voice against the use Animegao. A correction which was unfortunately over-ridden by notable Wikipedia editor Bryan Derksen.
Going further along towards 2007 user KurisuTsurifu attempted to once again correct the page, noting "Did some research into the term Animegao. Through both google searches, and talking to Japanese Anime Character Kigurumi players, Animegao refers to the anime-faced dolls, not the anime-faced cosplay".
Unfortunately by this point a dedicated "Animegao Kigurumi" page had already been created, and the term for better or worse had been essentially canonized by an anonymous editor with zero sources. This lead to shifting the burden of proof as the onus on disproving the invented term fell to newer contributors, making it essentially impossible to correct without significant effort.
Indeed even in the Talk Page on Wikipedia for Kigurumi, the term is contested with no clear resolution, and the Animegao Kigurumi article's talk page similarly covers that this is a term that is not used in Japan and questioning the validity of the term. Further more on the Japanese Wikipedia the validity of the term Animegao Kigurumi is put into question as being an invented foreigner term.
Bishoujo Kigurumi
As linked above referring to the Japanese Wikipedia page, Bishoujo Kigurumi (美少女着ぐるみ), literally "beautiful girl costume (kigurumi)" is the traditional term for anime styled kigurumi, or kigurumi masks as we typically refer to them in English.
By virtue of being the traditional term used in Japan, it is the term you will find most historical sites and records of Kigurumi masks.
Thesis on Animegao Kigurumi
This section in specific is the sole opinion of the admin of this wiki
From what details we do have on the term アニメ顔 (animegao), the first clear usage of it being on Wikipedia, and the context of the user's other edits, I believe this term was created in an attempt to capitalize on the term Kigurumi, for use towards what we in the west would call a fursuit.
Terminology was still fresh back then for many an emerging space, and Kemono/Furry was no exception. "ファースーツ" is a transliteration of fursuit, and while kemonā did exist as a term, kemono style kigurumi costumes were still in their infancy as a hobbyist space. The term Kigurumi covers multiple genres of full body costumes, and it isn't unreasonable to see how some may have wanted the term to specifically be used for their preferred genre.
I do agree some with the Wikipedia user KurisuTsurifu and their attempted edit in 2007. I dont think its a stretch to assume the doll connection was made when coining "animegao kigurumi" and the anonymous Wikipedia user wanted to use generic terms doll fans were using to differentiate between anime and not, likely not aware that bishoujo kigurumi was a term that was already in use.
Anyways, thats my theory, my Animegao theory.
Have any literature or sources we missed? Please, please absolutely let us know!