I can ' t believe they fell for that ! Oldest trick in the book p <| sep |> It ' s not the monotheism that ' s problematic with the Abrahamic faiths It ' s that ordinarily they ' re exclusive . Each of them has a doctrine that says the given faith is the only correct way to believe . There are other faiths that have the same exclusivity clause to them , but Christianity , Judaism , and Islam are the biggies . But Japan has basically said If you want to operate as a religion within our borders , you have to leave that exclusionary crap out of it . We ' re not having it . We will believe in Jesus AND Buddha if we want , and you can ' t do a damn thing about it ! I think certain liberal variations of Christianity are more flexible about it , so they ' re allowed to assimilate . Islam as practiced today is nowhere nearly as flexible , so there are barely any Muslims in Japan at all , and almost all are foreigners . I ' m not sure why Japan ended up so pluralistic whereas South Korea ended up much less so , i . e . , most Koreans who call themselves Christian about 30 % of the population also renounce , or at least claim not to follow , other Eastern religions .