Yukkuri
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-''":::::::::::::｀''＞ Please take it easy!!! ＜
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（ ,ﾊ ヽ _ﾝ 人! | ||ヽ、 ,ｲ| ||ｲ| /
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Yukkuri (ゆっくり) are adorable creatures that resemble the disembodied heads of Touhou Project characters. Originating as an AA meme, they became the subject of fanart, and even have their own lore.
Yukkuri AA
Around 2007, someone posted AA art of the characters Reimu and Marisa saying "Yukkuri shite itte ne!!!" (ゆっくりしていってね！！！) meaning "Please take it easy!!!". Some people thought it looked kind of silly, as if the characters were round disembodied heads, and joked about them being Manjū buns. They quickly became a meme in the Touhou fandom, and yukkuri versions of all the different Touhou characters were created.
Yukkuri Lore
While some people found the yukkuri cute, and drew tons of fanart of them, others didn't, and portrayed them being tortured in abuse scenarios. Either way, people were talking about them, and soon there was lore behind them. You can read about this lore in more detail on the Yukkuri Wiki.
Yukkuri are living Manjū buns, that come in different types based off of different Touhou characters. The filling they have depends on what type of Yukkuri they are (eg. Yukkuri Reimus are full of red bean paste). Anything they eat is magically converted into filling. The more a yukkuri suffers, the sweeter its filling tastes.
Since they don't have arms or legs, Yukkuri usually move by jumping, and sometimes can use their hair to hold things. They can even do things like make buildings and dig their own burrows in the wild. Their ability to easily do all this without any limbs is sometimes explained as a supernatural placebo effect1. They can also smell and hear, despite not having noses or ears.
Yukkuri are very silly, and have an extremely poor grasp of logic. They can usually be divided into "niceheads" (friendly yukkuri) and "shitheads" ("mean yukkuri"), but they all suffer from "Yukkuri logic" which can mess with their sense of right and wrong. Taking it easy is a big part of their philosophy.
Although they are usually based off of Touhou Project characters, yukkuri versions of other characters sometimes exist. Wild yukkuri are often seen by humans in-universe as pests, but they also can make good pets.
Similarity to Fluffy Pony Lore
While studying yukkuri lore, it occured to me that the yukkuri fandom is Fluffy Pony fandom. Both are based off of lore created by an already existing fandom (Touhou Project and My Little Pony respectively), but are quite different from the source material. Both involve the misadventures of adorable, yet extremely stupid creatures. Both often involve said creatures being brutally tortured by humans, but there can also be wholesome content where they are kept as pets. Yukkuri were created by 2chan, fluffy ponies were created by 4chan, I could go on.
To my knowledge, these two fandoms sprung up completely independently of each other. While there is some recognition of yukkuri in the west, it hasn't really left the Touhou fandom. Meanwhile, fluffy ponies don't seem to be very well-known at all, even in the larger My Little Pony fandom.
1 Sometimes referred to as "Belief Power" or "Yunhausen Effect". Compare Ork Technology from Warhammer 40,000, which miraculously works solely because the orks using it believe it does.
