Yamato no Aya clan (東漢氏) was an immigrant clan active in Japan since the Kofun period according to the Nihon Shoki (720), Kojiki (711) and Shoku Nihongi (797).
Origins
According to ancient Japanese records, Nihon Shoki and Kojiki, Yamato no Aya clan was one of the many clans that arrived from the Korean kingdoms during the reign of Emperor Ōjin.
It is said that the clan started off small but gradually grew as other clans integrated themselves to the clan, later becoming one of the most influential clans in Japan.
According to Teiji Kadowaki at Kyoto University, the name "Yamato no Aya" was widely used by Korean immigrants to apply dominance in their newly found home. Similarly with the Hata clan from Silla being wrongfully credited as a kingdom from Qin Dynasty, Yamato no Aya clan is thought to have been misinterpreted as a clan from Han Dynasty and was wrongfully credited as such when in fact, they were originally from Baekje.
It is also said that "Hinokuma no Sato (檜前郡鄕)", present day "Hinokuma (檜前)" of Nara prefecture was a place Yamato no Aya clan had jurisdiction over as well as being a well-known "Baekje town" also known as "Kudara no Sato (百済の里)" in Japanese.
The misconception seems to have stemmed from Shinsen Shōjiroku, an imperially commissioned Japanese genealogical record that unintentionally listed unknown clans of Korean origins as "Kan (漢)". Where "Kan" is written as the Han Dynasty in on’yomi, but in truth were families who could not identify with the other four Korean kingdoms (Goguryeo, Baekje, Silla and Gaya) also known as "Kara (漢)" in kun’yomi. For instance, at the end of the 8th century, a warrior of Korean descent named Sakanoue no Karitamaro (坂上 田村麻呂) created the Yamato no Aya clan and in an attempt to give credence he claimed his ancestor Achi no omi (阿知使主) to come from "Kan", which is why his clan is recorded in the book under "Kan".
For further context, in Old Japanese, Ancient Koreans (and things deriving from Korea) were called "Kara (から)", which under the same kun’yomi used three separate characters "韓", "漢" and "唐". The etymology is thought to have been derived from the "Gaya Confederacy" which was known as "Kara (加羅)" in Ancient Japan which later on adopted the aforementioned characters (韓/漢/唐) to represent Korea (and later on China or in general, lands outside of Japan). In Old Korean, Ancient Koreans used two characters of Han (using eumcha/음차), "韓" or "漢" (and to less extent "幹" or "刊") to describe themselves since both words shared the same pronunciation "한 (Han)" meaning "big" or "great" in native Korean which is thought to have derived from the now obsolete adjective "~하다 (Hada)" of the same meaning. Though now obsolete, such is evident in "Jinhan (辰韓)", "Byeonhan (弁韓)", "Mahan (馬韓)", "Hanguk (韓國)", "Hallasan (漢拏山)", "Han River (漢江)", or in "Hanseong (漢城)" an old name for Seoul. On top of place names, Korean used "漢 (Han)" to describe something that was big or have matured as evident in "황소 (Hwangso)" meaning bull evolving from "漢쇼 (Han-sho)" which meant "matured cow". Some place names also carry the meaning as seen in "Hallasan (Reaching big sky Mountain)", "Han River (Big River)" and "Hanseong (Big city/Capital)". All mentioned characters are used separately from Chinese Han (state), Han (Western Zhou state), Han Dynasty, Tang Dynasty and the Han Chinese which also use the same characters in respective languages.
Relations with the Aya clan and other immigrant clans
Japanese scholars have indicated that Yamato no Aya clan and other "Aya (漢)" clans were all related and that they were generally classified under the same ethnic group. These mainly included: the "Aya clan (漢氏)", the "Yamato no Aya clan (東漢氏/倭漢氏)" and the "Kawachi no Aya clan (西漢氏/河内漢氏)". It is said that Yamato no Aya, Aya and Kawachi no Aya, though not from the same founder, were ethnically related, most likely all immigrating from Baekje.
"Kawachi no Aya (西漢氏)" in particular, is thought to be related with the Yamato no Aya clan. The clan was one of the clans first founded by the scholar Wani (alongside clans such as "Kawachi no Fumi clan (西文氏)") who arrived in Japan from the kingdom of Baekje who helped spread the use of the Chinese Writing system in Japan.
Yamato no Aya clan also had a related clan called the "Sakanoue clan (坂上氏)" (the clan that Sakanoue no Karitamaro hails from) which was once part of the bigger and more influential Yamato no Aya clan, but later broke off to form a clan of their own.
After the formation of the clans, the next immigrants were mainly called "Imaki no Ayahito (今来漢人/新漢人)" .