http://www.nestorian.org/christianity_arrived_in_japan_.html

JAPAN CHRISTIANITY ARRIVED IN JAPAN CENTURIES BEFORE SAINT XAVIER, SCHOLARS SAY

Contrary to popular lore, Christianity in Japan dates back centuries before the 1549 arrival of Jesuit missionary Saint Francis Xavier, a Christian evangelist and other researchers claim.
American Reverend Ken Joseph told a gathering here on March 16 that Christianity first came to the Far East roughly 1,800 years ago along the "Silk Road," passing through China to Nara, central Japan.
Evidence of this, Reverend Joseph said, was a copy of the Gospel of Saint Matthew in old Chinese script, dating back to the ninth century, found inside the Koryuji Buddhist Temple in Kyoto, near Nara.
This temple is cited by at least one historian as having been built about 818 atop a Christian building erected in 603 that was destroyed by fire.
"Many Buddhist temples were built on top of old, burned down Christian churches left in ruins. Diligent research today can still uncover these lost relics," Reverend Joseph said.
Researcher M.L. Young says that one of the most sacred objects of the Nishi Honganji Buddhist Temple, founded by Kobo Daishi in 806 after his contact with a Nestorian Christian monastery in Beijing, is "the Lord of the Universe's Discourse on Almsgiving," a commentary on the Sermon on the Mount and other Matthean passages.
Christianity was referred to as the "luminous religion" in Chinese records referring to Nestorian missioners.
Reverend Joseph presented slides of several artifacts and statues that once had Christian crosses carved into them, but which had subsequently been erased or modified by Buddhist followers, he alleged.
Nestorian Christianity dates back to the first century of the Christian era.
Japanese researchers say that the first bearers of Christianity to Japan were the people from the  (Nestorian) Assyrian Church of the East who came to Japan from the Silk Road cities of Mesopotamia, and Persia starting around the fifth century onwards.
"Christianity was much more widespread than believed," Hollingsworth said.