Shinto
[Joseph Campbell] was in Japan for a conference on religion, and he overheard another American delegate, a social philosopher from New York, say to a Shinto priest, "We've been now to a great many ceremonies and have seen quite a few of your shrines. But I don't get your ideology. I don't get your theology."
The Japanese paused as though in deep thought, and then slowly shook his head. "I think we don't have ideology," he said. "We don't have theology. We dance."—Bill Moyers
Shintō (神道) or Shintoism, was the original religion of Japan and the Japanese people before Buddhism came along. Essentially, it's a set of practices, to be carried out diligently, to establish a connection between present day Japan and its ancient past. Shinto today is a term that applies to public shrines suited to various purposes such as war memorials, harvest festivals, romance, and historical monuments, as well as various sectarian organizations. It's notable for being rather light on philosophizing and heavy on community spirits.
According to the Creation Story, the gods Izanagi-no-Mikoto and Izanami-no-Mikoto were tasked with creating Japan by the first gods, Kunitokotachi and Amenominakanushi. Using the sacred jewelled spear, they created Onogoro Island, and made their home there. When they wished to be married, they build a palace with a pillar in the middle, and walked around the pillar in opposite directions. When they met, Izanami spoke first, and gave birth to Hiruko, the deformed leech-god of fishermen. They walked around the pillar again, and this time Izanagi spoke first, and Izanami gave birth to the islands of Japan, among many other gods. Tragedy struck when Izanami gave birth to Kagutsuchi and was burnt to death in the process. Izanagi sliced Kagutsuchi to pieces, and the pieces became dozens of lesser deities. He travelled to Yomi, the underworld, to retrieve his wife, but saw she had become a rotted corpse and fled in terror. Izanami, enraged, swore to kill a thousand humans, and Izanagi vowed to create 1500 to take their place. To cleanse himself. Izanagi washed his face, and from his right eye, left eye, and nose, respectively, the sun goddess Amaterasu, moon god Tsukuyomi, and storm god Susanoo were born.
Amaterasu became The High Queen of the gods and the ancestor of the emperors of Japan, but had issues with her brother Susanoo. To escape his rages, she once hid herself away in a cave, forcing the other gods to coax her out to prevent The Night That Never Ends. When Susanoo raped her attendants and violated her temples, Amaterasu cast him out of the heavens. Susanoo became The Atoner, wandering Japan until he came across a family of minor earth deities plagued by the Yamata no Orochi, a dragon with eight heads and eight tails, to which they had fed seven of their eight daughters. Susanoo fell in love with the last daughter, Kushinada, and disguised himself as her, tricking the Orochi into getting drunk on sake and killing it. Inside its body, he found the Ama-no-Murakumo, which was later renamed the Kusanagi. He married Kushinada and presented the Kusanagi to his sister as a peace offering and was accepted back into the heavens.
Actually, scratch those bits about the gods in their high heavens, because these are the matters of people in the capitol. Shinto is a catch-all term for largely-unconnected folk beliefs across the different places in Japan. Some gods might be popular nationwide such as The Seven Gods of Fortunes, but where there is a Shinto shrine, there is a local deity enshrined that only influence its immediate areas. People would pray to that god and throw a festival to honor it (or just to make a festivity, it's not like there were televisions to alleviate boredom in ancient Japan).
Religious practices are thus different between places. The favored practices of god A are not likely to be the favored practices of god B, the same applies to taboos. But some common patterns exist, such as not visiting a shrine when you're "tainted" (i.e. one of your close relatives just recently leaving this mortal coil, you just touched a dead body, or you're a woman in that certain time of the month).
Shinto coexist easily with other religions. It's sharing the space in people's heart with Buddhism and Taoism. It's not unusual for a Japanese to start life in Shintoism as his or her name is registered in the nearby shrine, to be acknowledged by the local gods as the new member of the community; then hold a marriage the Western (Christian) way[1]; then leaving this world as a Buddhist with a Buddhist funeral.
See also Miko, Shrines and Temples, Onmyodo, Buddhism, Ofuda, Youkai, Religion Is Magic. Compare Wicca, Druidism, and Heathenry, for similar animistic folk practice.