To go to Japan, is to arrive in a country where spirituality and religion are deeply rooted. If the large majority of Japanese are Shintos, many are also Buddhists; Christian, Muslim and Jewish religions are also represented to a lesser extent.
Shintoism is the main religion in Japan (84% believers). It's linked to the oldest cult forms (shamanism, animism) from the archipelago, as well as a reverence for nature, which have combined and codified over time to become Shintoism.
Buddhism arrived later, from the 5th century onwards, imported from China and Korea. It was the need to pass on its teachings which pushed the Japanese to develop a written language.
Today, 71% of Japanese call themselves Buddhists, a figure which can seem astounding when coupled with the striking number of Shintoists in the country. Yet, the Japanese have a fairly free vision of religion and they often practice several in a lifetime, sometimes at the same time. Many identify with the values of the two main religions in the form of an old syncretism: Shinto-Buddhism.
Christianity (2% of the population) had a flourishing development for half of the 16th century, but its banning (from 1614 to 1854) caused its decline. Nevertheless, it's still the third most represented religion in the archipelago.
About 8% of people have other beliefs; there are 100,000 Muslims (of which 10% are Japanese) and a Jewish community which arrived in two waves. The first came from Syria, Yemen and Iran (around 1850) to do business after the end of the economic blockade. The second came from Russia (from 1917 to 1920), when fleeing the civil war.
Finally, a large number of sects were established in the 20th century, but this term doesn't have the negative connotation in Japan that it has in Western cultures.