Absolutely fascinating Metafilter post about Otokichi, or 山本 音吉 (Yamamoto Otokichi, later known as John Matthew Ottoson) which points to The Otokichi Story, a biography of a very unusual Japanese man.
Otokichi highlights & accomplishments at a glance
・ First Japanese in America (Preceded John Manjiro by 10 yrs and John [Joseph] Heco by 30 yrs)
・ First Japanese in Canada
・ Payload of Setoyaki represented first trade between U.S. and Japan
・ Inspiration for Commodore Perry (opened trade with Japan)
・ Probable inspiration for Ranald MacDonald (first American in Japan), from Astoria Oregon 1840s
・ First Japanese to gain British Citizenship
・ First trilingual in Japanese, English and Chinese
・ First Japanese in Royal British Navy
・ First Japanese Christian (Protestant Episcopalian)
・ Translated Bible of John into Japanese
・ Opened Nagasaki Port on behalf of the British Crown in 1854
It is the hopes of the authors that the individuality and sense of adventure shown by Otokichi - in the face of incredible challenges - will inspire a generation of Japanese to take their destiny into their own hands.
I'm pretty sure lots of Japanese were converted to Christianity in the Sengoku period by the (mainly) Jesuit missionaries.