After his studies in China, Saicho established the Japanese Tendai School with its headquarers on Mt. Hiei. A special feature of this school，the incorporation of tantric elements, was further developed by Saicho's disciple En-nin and later on by En-chin and An-nen. In 838 CE，En-nin went to China for a stint as a "monk requesting for instruction" but certain circumstances prevented him from the pilgrimage to Mt. Tientai，yet when he tried to return to Japan strong winds forced hime to stay in China. He thereupon travelled to Mt. Wutai，Chang'an and other places and studied with famous masters the teachings of both the Tientai and Tantric Schools. During his stay，he went through Emperor Wuzong's persecution of Buddhism which forced him to return to lay life for some time.After his return to Japan in 847 CE，he recorded his experiences in the Nitoguhojunreigyoki. In doctrinal respect，he composed among other works the Kongochokyosho and Soshitsujikyoryakusho arguing for the supremacy of the tantric teaching over the Tendai Perfect Teaching. In his view，the Tendai School which based itself primarily on the Lotus Suutra did not belong to the exoteric schools but to the esoteric.Nevertheless it was on a lower level than the esoteric school which mainly used texts like the Dari jing and Jin'gangding jing because the Lotus Suutra, despite talking about the "noumenal secret" of relative and absolute truths being identical and inseparable，did not mention the "phenomenal secret" of the "three secrets"of body，speech, and mind which were expounded by Buddha Vairocana and are mentioned in the Dari jing and Jin'gangding jing. Moreover，based on the concept of Buddha nature inherent in every human being，En-nin further developed the idea of "attaining Buddhahood in this very body"，one of the basic teachings of the esoteric schools. According to him，any ordinary worldling was in a position to quickly achieve Buddhahood in this very life provided he practiced the "three secrets" seriously.En-nin also introduced Fazhao's wuhui nianfo to Japan. This pure land practice which he had learnt on Mt. Wutai exerted reat impact on the rise of pure lan devotionalism at Mt. Hiei.
