Silence by Shusaku Endo (1966)
If I understand it correctly, Christians did make some inroads in Japan, but then the Japanese government banned Christianity in the 17th century and punished those who still worshiped Christ. Many missionaries left, but some still tried to serve underground. If the officials found Christians, they were forced to denounce their religion and become an apostate or were killed. As far as I got into the book, two Portuguese fathers hear of their teacher having apostatized and don't believe it, so they sneak into Japan and find a few Japanese villages that still have Christian believers that they serve. I am sure they were going to go look for their teacher and discover what has happened to him.
I just could not continue listening to this, as in my mind I kept asking "why are you doing this?" The only slight glimpse of understanding I got was from a line where the Japanese told the missionaries that the Christian fathers were the only ones that treated them like human beings, with love and care. I understand their lives were harsh, as were those of lower classes everywhere, and I get that religion offered hope, something to help people get through the hard times. I would rather explore why Buddhism did not offer that to the people of Japan.