the aging population in Japan is shrinking for some years now and will continue to do so. Since religious groups reflect the demographics of their society they will shrink too.
The aging of Japan is thought to outweigh all other nations, as
the country is purported to have the highest proportion of elderly
citizens; 33.0% are above age 60, 25.9% are aged 65 or above, 12.5% aged
75 or above, as of September 2014.