Cross-cultural Servanthood by Duane Elmer. Duane Elmer asked people around the world how they felt about Western missionaries. The response? “Missionaries could be more effective if they did not think they were better than us.” The last thing we want to do in cross-cultural ministry is to offend people in other cultures. Unfortunately, all too often and even though we don't mean it, our actions communicate superiority, paternalism, imperialism and arrogance. Cross-cultural specialist Duane Elmer gives Christians practical advice for serving other cultures with sensitivity and humility. He offers principles and guidance for avoiding misunderstandings and building relationships in ways that honor others.
The following books would serve as excellent gifts for your Japanese friends.
Love From the Depths the Story of Tomihiro Hoshino by Tomihiro Hoshino. The autobiography of a famous Japanese Christian artist who also happens to be quadriplegic, due to a gymnastics accident.
Shiokari Pass by Ayako Miura, translated by Bill & Sheila Fearnehough. A wonderful novel illustrating sacrificial love. This novel was a bestseller and was even made into a feature film. Ayako Miura was a popular novelist and poet who presented Christianity in a positive light, opening up many Japanese to the gospel. She has written many other books, too (道ありき、氷点、etc.).
Religions of Japan
Shinto the Kami Way by Sokyo Ono. An explanation and overview of Shinto.
Talking about Buddhism in English by Yoshihito Takada & James Vardaman. The best and most easily understandable presentation of Japanese Buddhism.
Sermons of a Buddhist Abbot: Addresses on Religious Subjects by Soyen Shaku and translated by D.T. Suzuki. Reprint of Sermons of a Buddhist.
Beyond Buddhism: A basic introduction to the Buddhist tradition by Isamu Yamamoto. This is the best overview of Buddhism available from a Christian perspective.