Hi!
Not true. While in the past, there may have been a larger Christian following in Japan,
Actually, the large Christian following would have been very unlikely at least before World War II: Christianity was understood as a threat to the independence of Japan in the 17th century and was punishable BY DEATH. This is also the reason why only the Dutch merchants were allowed later during that time - they were the only merchants who were really professionally and willing to do just trade without missionizing, as opposed to the Spanish or British. When the country was opened in the 19th century, while they did take over a lot of things from Europe and the US, at the core of it all was an extreme feeling of nationalism around a highly elevated conception of the emperor. Surrounding that nationalism, shintoism, which was basically a folk religion until then became much stronger codified (well, there had been official books on the history of the world in shintoist belief, but that was all) and rituals were made universal to it (for instance, the "traditional Japanese marriage ceremony" known today was basically invented in the 19th century). Shinto was basically made into an equivalent of Christianity (at least in the eyes of the Japanese) and became the state religion. And among the growing nationalism and militarism, Christianity was not really embraced.
However, there was indeed a small influx of Christianity because of foreign teachers used in Japan, who also happened to introduce the students to Christianity, but the regime made an effort to replace them with their own teachers and thus reduce that influence in due time.
Deathworks