12. Shinto (4 million adherents)
Shinto began as a Japanese creation mythology. Once upon a time, two gods were called by all the myriad gods to create a new land. They are Izanami and Izanagi. They were given a spear which they used to stir the water. Thus, Japan emerged.
Since then, Shinto became a way of life for Japanese people. Now, it is the largest religion in Japan. About 80% of Japanese population practice Shinto. However, most of them do not identify themselves as its adherents.
This comes from the difference of point of view towards the belief among them. Most of Japanese come to Shinto shrines to worship the gods not as a form of religion, but more of a tradition.
Shinto worships Kami as a sacred divine essence which can manifest in multiple forms. Thus, certain objects are worshiped and housed in the Shinto shrines.