What religion do most of the Japanese practice?
Mostly Buddhism and some Shinto. Japan is actually not a very religious country. A recent survey show that 52% of the people do not feel they belong to any religion, Buddhism (various sects) accounts for 35%, Shinto 11% and Christianity 11%. Very samll groups like th Ainu in the Northern areas have their own traditional worship.
The picture is further complicated by the fact that belonging to multiple religious groups is not uncommon, and some Japanese keep up a nominal association with a religion for ceremonies like marriage and funerals.