There are many organizations that provide opportunities for ministry to the Japanese people, both in the US and in Japan:
Mission to Japan
Mission To Japan seeks to bring the good news of the gospel to Japan through mission trips to Japan and through "homestay" programs. The homestay program allows Japanese students (usually ages 16 - 22) to come to the U.S. and stay with a Christian host family (usually for two to three weeks).
Okinawa Christian School International
OCSI is a non-denominational mission whose purpose is to partner with families of the international community of Okinawa by offering an excellent Christian education in the English language.
Equipper Conference '07
Equipper Conference is a five night conference which “equips” (Ephesians 4:12) Japanese Christians who met Jesus overseas for their eventual return to their home country as ambassadors of Christ.
Reaching Japanese for Christ
The Reaching Japanese for Christ Network (RJC) is a place for you to create synergies with other Christian believers who share a love for and interest in Japanese people, particularly those who come to North America on a temporary basis.
Friends of Nagoya Theological Seminary
Friends of Nagoya Theological Seminary's purpose is to support a theological seminary to be formed in Nagoya, Japan.