What is "shintoshu"

The is a Japanese story book in ten volumes believed to date from the Nanboku-chō period (1336–1392). It illustrates with tales about various shrines the Buddhist honji suijaku theory, according to which Japanese kami were simply local manifestations of the Indian gods of Buddhism. This theory, created and developed mostly by Tendai monks, was never systematized, but was nonetheless very pervasive and very influential. The book had thereafter great influence over literature and the arts.