Eison (1201 - October 6, 1290) was a priest of Shingon Ritsu sect during the mid Kamakura period. His azana (a popular name) was Shien. His shigo (a posthumous name) was Koshobosatsu. He was the son of 慶玄, a scholar priest at the Kofuku-ji Temple, born in Yamato Province. He is known as a priest who revived the precepts of Buddhism and restored the Nara Saidai-ji Temple (Nara City).
When he was 17, he studied under Eiken the Ajari (a master in esoteric Buddhism) of the Daigo-ji Temple and entered into the priesthood. Later he went into Mt. Koya to learn the Shingon Esoteric Buddhism, and in 1235, he became Saidai-ji Hoto-in Temple Jisai-so (a priest who keep one's purity by upholding religious precepts for Buddhist services at Saidai-ji Hoto-in Temple) intending to revive the precepts of Buddhism. In the following 1236, he made self-ordination at the Todai-ji Temple with Kakujo, Ensei, and Ugon, and went to the Kairyuo-ji Temple; then in 1237 he returned to the Saidai-ji Temple and made kekkai (to restrict a certain area to prevent priests from prohibiting the precepts) to revive the Ritsu sect.
He performed Jukai (handing down the precepts) and Monju Bosatsu kuyo (ceremony of offering to Manjusri); prohibited hunting and fishing in religious acts such as the Mantra of Light; offered charity and relief; and restored Uji-bashi Bridge. He accepted anyone's conversion to Buddhism regardless of their social standings, from Hinin (those in the lowest rank of caste system) and lepers to the Retired Emperors Gosaga, Kameyama, and Gofukakusa. He was invited by the regent Tokiyori HOJO of the Kamakura bakufu (Japanese feudal government headed by a shogun) and went to Kamakura to hand down and lecture on the precepts widely. He made great efforts to restore provincial monasteries and Hokke-ji Temple, and allowed the handing down of the precepts to nuns that had been prohibited for years. In 1282 when Saigen who was the Tendai-zasu (head priest of the Tendai sect) (Enryaku-ji Temple) disputed with Ryuben who was the Chori (chief priest) of Onjo-ji Temple, over the position of betto (steward) of Shitenno-ji Temple by supporting candidates of their own, Eison was appointed to the betto by an entreaty of the Imperial Court because he was not concerted in both parties. His disciples included Ninsho and Shinku.
Eison is generally known for his achievements in the revival of the precepts of Buddhism and the Ritsu sect, but his original intention was to revive priests of the Shingon sect from corruption caused by their overly close connection to the authorities. To achieve this aim, he had to start with a revival of the precepts that were the basics of education and learning of Buddhism, and the Ritsu sect that focused on a study of the percepts. While Ganjin (Jianzhen), the founder of the Ritsu sect in Japan, obeyed the Shibun-ritsu (Four-Part Vinayapitaka, which explains about regulations and prohibited matters of the priests), Eison obeyed the Juju-ritsu (Ten-Reciting Vinayapitaka) that Kukai, the founder of the Shingon sect, valued. Eison regarded a revival of the precepts and the study of Shingon Esoteric Buddhism as equally important, so he reprimanded his disciple Ninsho for being negligent of the study by being too enthusiastic about social activities and propagation in eastern Japan, and at the time of Mongol invasion attempts against Japan, he offered a prayer and ritual of Esoteric Buddhism at Saidai-ji and Shitenno-ji Temples to repel the Mongol Empirical army.
His books include 'Kanjingakushoki' and 'Bonmokyokoshakuki bugyomonju.'