Main religion in Japan is dominated by Shinto and Buddhism. Christian and other religion are still minor but it exists. Japan has been receptive western culture and events – Christmas, Valentines’ day and more! Not so many Japanese people knew about Halloween 10 years ago. And now Halloween event is one of the biggest event for a year now!
What about Easter? It is still not known as Halloween, however some big companies in Japan start to cerebrate Easter – Tokyo Disney land, Fuji-kyu High land and some snack companies (KitKat , Buskin Robbins and more!) So maybe 10 years from now, Easter will be a big deal for Japanese people.