An article with some bad English, from eurautarchy who has views on topics I couldn't agree with but who reproduced what follows on his website.
>Toyoko Morita: Iranian arrivals to ancient Japan
>The article below is by Toyoko Morita and originally appeared in the Encyclopedia Iranica. Morita’s article was originally published in print on December 15, 2008 and last updated on April 10, 2012. This article is also accessible in print Vol. XIV, Fasc. 5, pp. 558-560 and Vol. XIV, Fasc. 6, p. 561). The version published below has embedded photographs, paintings and accompanying captions that did not appear in the original Encyclopedia Iranica publication/posting.
>The first mention of Iranians (Persians) coming to Japan can be found in the Nihon Shoki (Chronicles of Japan), one of the earliest Japanese historical sources, completed in 720 C.E. It records that in 654 C.E. several people arrived in Japan from Tokhārā (Aston, pp. 246, 251, 259). Though there is some controversy about the location of Tokhārā, some scholars have claimed the name to be a shortened version of Toḵārestān, which was part of the territory of Sasanian Persia (Itō, 1980, pp. 5-10).
A link to the Tocharians seems very likely considering the geographical areas concerned with these peoples. More to this later on.
>The oldest document in Persian, which is preserved in Japan, was procured by the Japanese priest named Kyōsei (1189-1268) from Iranians (Persians) during his trip to southern Asia in 1217. Thinking they were Indians, the priest asked them to write something for him as a keepsake. However, after his return to Japan he found out that they were not Indians, because no one could understand what the writing meant. This document—a single page—was discovered in the late 20th century, when it was established that it is written in Persian and contains a line from Abu’l-Qāsem Ferdowsi’s Šāh-nāma (qq.v.), a line from Faḵr-al-Din Gorgāni’s Vis o Rāmin (qq.v.), and a quatrain of unknown authorship (Okada, 1989).
>Fresco along the Tarim Basin, China depicting an Iranian-speaking Buddhist monk (Kushan, Soghdian, Persian or Tocharian?) [at left] instructing a Chinese monk [at right] on philosophy (c. 9th-10th Century). Iranian peoples of Central Asia were the link between Asia as a whole and the civilizations of ancient Iran, notably Sassanian and post-Sassanian culture(s). Open and tolerant, the Soghdians, Kushans, Tocharians, etc. established a sophisticated literature and urban culture (Lecture slide from Kaveh Farrokh’s lectures from the course “The Silk Route: origins & History“).
>Elsewhere in the Nihon Shoki, it is mentioned that in 660, when an Iranian (Persian), whose name was Dārā, returned to his country, he left his wife in Japan and promised the Emperor that he would come back and work for him again (Aston, p. 266; Imoto, 2002, pp. 58-60).
>In the 7th to the 9th centuries, foreigners—then known in Japanese as toraijin—were coming to Japan mainly from Korea and China, bringing with them technology, culture, religion (Buddhism), and ideas. Eastern Asia, especially the Tang Dynasty of China (618-907), had socio-economic networks with many regions of the world, including southern and western Asia.