There are several influential and notable Japanese Christian men and women during the Meiji, Taisho and Showa periods and generally at the time the Empire of Japan was around which is the time period you seem to be asking for.

Many Japanese Christians served important military and government positions in the Empire of Japan such as Yōsuke Matsuoka, a Presbyterian Christian who was the Minister of Foreign Affairs of the Empire of Japan during the early stages of World War II.

This mystery guy you are probably looking for is Nitobe Inazō. If there is any other guy that fits the picture more than him, I don't know who he is, but Nitobe Inazō is fine and fits most of the details you provided.

Nitobe Inazō was a notable author in the Taisho and Showa periods and wrote a lot of books and scholarly works. The book that he wrote you are probably looking for is Bushido: The Soul of Japan published in 1900, one of the first major works in samurai ethics and Japanese culture. The book was written in English originally to be intended to be read by a Western audience.

Nitobe Inazo in his work cited the similarities between the pillars of Japanese culture such as Shinto, Confucianism and Buddhism and the roots of European and American cultural traditions such as Roman, Greek and Biblical Judeo-Christian culture and cited a lot of Western philosophers and statesmen and compared the Japanese Bushido with medieval chivalry in the West and Ancient Greek culture.

Regarding his religion, Nitobe Inazo had ties with Protestant Christian groups and the Quaker movement. Nitobe was baptized in the American Methodist Episcopal church by a missionary, and after traveling to the United States to study economics and political science he became a member of the Religious Society of Friends or Quakers.

As Nitobe Inazo's works are now in the public domain, his book Bushido: The Soul of Japan can now be read for full, free and online here: http://www.gutenberg.org/files/12096/12096-h/12096-h.htm