One of the two major schools of esoteric Buddhism in Japan (the other is Tendai) introduced from India via China by the Japanese monk Kukai (774—835) a Buddhist master and culture-hero better known by his posthumous name of Kobo Daishi. Shingon Buddhist ideas about the identity of this phenomenal world with the realm of enlightenment fostered Japanese genius in the development of art and ritual and enabled the easy assimilation of kami and local spirits into the Buddhist world-view (see Ryobu Shinto). Shingon esotericism was and remains an element in the mountain-religion shugendo which combines worship of kami and Buddhas. Until 1868 the imperial family were Buddhists who belonged to the Shingon school and carried out Buddhist memorial rites for their ancestors. Their patron temple was Sennyuji in Kyoto. Connections between the Imperial family and Buddhism, and between shrines and Shingon, were severed at the time of the Meiji restoration, when the Emperor started to visit shrines.
A Popular Dictionary of Shinto. Brian Bocking.