Japanese people consider themselves most as Buddhist and Shinto Believer. But they are not so religious at all. They go to Cristian church in the Christmas and go to Shrines and Temples on the New Year Day. People wed in Christian Churches or Shinto Shrines to Buddhist Temples depending what they feel like.
Because they do not belong to one religion, they don't have much opinion about any other religion either. So when you see Japanese people praying at temples or shrines, do not think they are very religious. In many cases, they are praying "JUST IN CASE" most of the times.