The two chronicles that carry the kami mythology were commissioned by the court, within eight years of each other, and they do not agree. That disagreement is the most instructive thing about them.
The Kojiki, presented in 712, and the Nihon Shoki, completed in 720, tell the same broad sequence differently, and the Nihon Shoki habitually records variant versions side by side with the formula that another book says otherwise. A tradition that preserves its alternatives in the same volume is telling the reader something about how settled it was.
Both were produced to serve a political need: to establish the descent and legitimacy of the ruling line at a moment when continental models of statehood were being adopted wholesale. They are therefore excellent evidence for eighth-century court theology and much weaker evidence for what anyone in the provinces had been doing.
Two other bodies of material partly correct that. The fudoki, provincial gazetteers ordered at the same period, record local deities and place legends that the chronicles ignore. The norito, the liturgical addresses preserved in the tenth-century Engishiki, are the actual words of ritual rather than narrative about it.
Finally, the long entanglement with Buddhism has to be held in view. For most of Japanese history kami and buddhas were worshipped in the same institutions under theories that identified them, and the separation of the two was imposed by government in the nineteenth century. Much of what is now presented as ancient and purely Shinto dates from that separation.