Prince Shotoku (574-622). This is the prince who unified Japan under a blend of Confucian, Shinto, and Buddhist ideas but placed Buddhism at the top of the religious hierarchy, establishing a network of state-sponsored temples throughout the land. Several commentaries on Buddhist sutras are attributed to him, as well as works which are thought to reflect his understanding of Buddhism. The period of Prince Shotoku's activity is the Asuka Period (552-645)
Jianzhen (Jpn. Ganjin) (688-763). Jianzhen was a Chinese Vinaya master who was asked to come to Japan to establish ordination platforms and direct the ordination and training of monks in Japan. He is responsible for the establishment of such temples as Toshodaiji in the then capital of Japan, Nara. It took him six tries to make the crossing to Japan, and the extreme conditions of his attempts rendered him blind by the time he succeeded. Jianzhen, or as he is known by the Japanese reading of his name, Ganjin, spearheaded the development of Buddhism in the Nara Period (710-794). (For those who are interested in his efforts, a historical novel based on the lives of Ganjin and his contemporaries is available in English translation: Yasushi INOUE, The Rooftile of the Tempyo, tr. E. Seidensticker [Tokyo: Univ. of Tokyo Press]).
Saicho (767-833). Saicho was an official Japanese emissary to T'ang China and spent two years there studying various teachings including Hua-yen and Zen, but he focused on T'ien-t'ai (the school of Chih-i) and returned to Mount Hiei near the new capital of Japan Kyoto to establish the Japanese Tendai school. He called for a return to the spirit of practice rather than ritual formalism and the implementation of the 48 bodhisattva precepts rather than the full 250 and 348 precepts of the Vinaya. Together with Kukai, Saicho spearheaded the development of Buddhism during the Heian Period (794-1185).
Kukai (774-835). Like Saicho, Kukai went to T'ang China to study Buddhism and Chinese culture, but he went in a less official capacity and was therefore freer to pursue his own interests. Because of this, he was able to study more extensively the philosophy of esoteric Buddhism (Ch. Zhenyuan) and established the Japanese Shingon school on Mount Koya. Kukai is known as both a spiritual adept and a philosopher, a Buddhist monk and a cultural figure who contributed to the development of the Japanese language in its written forms, importation of Chinese literary, artistic and architectural forms, as well as new forms of religious thought and practice.
Shingon (Ch. Zhenyuan) Esoteric Buddhism (also known as Mantrayana). The main sutra of the Shingon school is the Dainichikyo (Skt. Maha-vairocana-sutra), or the sutra of the Great Sun Buddha, probably compiled in India around the seventh century. Esoteric Buddhism (which has its roots in the synthesis of early Indian Buddhism and other forms of indigenous Indian religion) is so-called because its teachings are hidden or secret in contrast to the exoteric or explicit teachings of the philosophical schools, Zen, and Pure Land. In Esoteric Buddhism, the true meaning behind the words of scripture can only be discerned when sufficient insight has attained, and texts themselves are only transmitted to those who have been properly initiated, both as a precaution to the student and in order to protect the teachings from abuse. The extensive use of mantras and dharanis, or multi-syllabic incantatory expressions, mandalas, the affirmation of life in this world, and extensive use of rituals and ritual implements are characteristic of Shingon esotericism.
Three mysteries of body, mind, and speech. "Three mysteries" is a rendering of sanmitsu kaji, or the three hidden modes of the ways in which the life of the practitioner is expanded by power of the Buddha. Through the various ritual practices of Shingon Buddhism, such as the oral invocation of mantras, the mental visualization of Buddhas and mandalas, and the physical enactment of various meditation postures and gestures (mudras), the power of the Buddhas' awakening is conferred upon the practitioner. These practices accelerate the process of awakening, and so Kukai taught that buddhahood could be attained in this very body (sokushin jobutsu). While speech is important in all schools of Buddhism, emphasis is often placed on mind and body, with speech and language generally regarded as an aspect of mind. However, Shingon Buddhism places great importance upon speech and the use of mantras and dharanis.
The dharmakaya which expounds the dharma. The converse of the three mysteries is the idea of hosshin seppo, or the idea that it is the dharmakaya, the formless, empty, ultimate body of the buddha that directly expounds the dharma, rather than the nirmanakaya, or the buddha in the physical body such as that of Sakyamuni. That is to say, the scriptures and practices of Shingon Buddhism are regarded by Kukai not so much as acts of the practitioner but as the direct expression of the ultimate reality of awakening.