The human heart is convoluted and there’s no sense to it as Jeremiah wrote, but I tried nevertheless. Thirty minutes with Google is supposed to give me the answer even though I’ve never been to Japan, know no Japanese, and know nothing of its culture. But... your heart can’t not go out for them: aging population with few babies, slaves to work after once they were slaves to the emperor, stone-cold killers during WW2 but now in a pacifism profound enough to have seemingly given up the fight altogether.
The chief impediments to Christianity there now seem to be a combination of factors:
1. Christianity is perceived as an import, as a “Western religion” and Japan is nationalistic. “Japanism is essentially a magico-shamanistic ritual/belief and ancestor worship. Also the belief in the uniqueness of Japan and its people, the ethno-centrism that is all-pervading, is called ‘Japanism’.” (From book “Jesus for Japan”).
2. General distaste for religion in general due to emperor-worship in WW2.
3. Tepid lukewarm felt banners Catholicism. Distaste for “hard teachings” on sexuality. Little to no celebration of extraordinary form.
4. 17th century persecutions that worked “enough”, much like persecutions in the USSR have worked “enough” to tamp down religious belief.
5. Surreal work ethic. Oblate of Mary missionary says “People don’t have time to come to Church. Here, work gets the priority, not religion.” (I’d love to know genesis of this. A result of aftermath of WW2 and scarcity? Or perhaps an aging population must work much harder due to decreasing productivity just to stay even?) From Japanese Catholic bishops statement: “Shared meals are rare...Consequently, there are no opportunities to share conversation. Each member of the family faces difficulties, but since there is no fellowship each is lonely and has little experience of loving or being loved."
6. Discouragement. High suicide rate. “Many Japanese suffer from a lack of healthy self-identity....Eternal life is not actually a happy idea to a Japanese. ‘Jesus will give you eternal life!’ No, thanks, thinks the Japanese, that is just what I want to avoid.” (book “Jesus for Japan”).