Keichu (1640 - March 4, 1701) was a priest of the Shingonshu sect and a Japanologist (Kokugaku [national study] scholar) who lived in the mid-Edo period. He was born in Amagasaki, Settsu Province (present-day Amagasaki City, Hyogo Prefecture). He was also called Keichu SHAKU. His secular family name was Shimogawa, and his azana (courtesy name) was Kushin. His grandfather Motoyoshi SHIMOGAWA served as a vassal to Kiyomasa KATO, and Keichu's father Mototsada was initially a feudal retainer of the Amagasaki clan but later became a ronin (samurai who left his master and lost his horoku [salary]).
As a little child, Keichu studied under Kaijo of Myoho-ji Temple in Imazato, Ozaka (present-day Osaka City), thereafter being ordained an Ajari (a master of esoteric Buddhism; a high priest) at Mt. Koya. After becoming an Ajari, Keichu became a Juji (chief priest) of Mandara-in Temple in Ikutama, Ozaka, where he interacted with Choryu SHIMOKOBE, but Keichu, who disliked secular affairs, went on pilgrimage within Kinai region (provinces surrounding Kyoto and Nara) as he went back to Mt. Koya. After returning to Mt. Koya, he stayed with Shigekata FUSEYA in Man-cho Village, Ikeda-go, Izumi Province (present-day Man-cho, Izumi City, Osaka Prefecture), reading a number of Japanese classics. After serving as a Juji of Myoho-ji Temple, Keichu lived his last years at Enju-an hermitage in Kozu, Settsu Province.
Keichu was a prolific writer, whose works included "Manyo Daishoki" (Commentary on Manyoshu [Collection of Ten Thousand Leaves]), which was entrusted to Keichu by Mitsukuni TOKUGAWA, "Kogan-sho" (Commentary on Verses in Kojiki [A Record of Ancient Matters] and Nihonshoki [Chronicles of Japan]), "Kokin Yozai-sho" (Commentary on Kokin Wakashu [Collection of Ancient and Modern poems]), "Seigo Okudan" (Conjectures on Ise Monogatari [The Tales of Ise]), "Genchu Shui" (Addenda to Commentary on the Tale of Genji), "Hyakunin Isshu Kaikan-sho" (Rectified Commentary on One Hundred Poems by One Hundred Poets), and "Waji Shoran-sho" (Corrections to Errors in Japanese Characters). Keichu established an empirical study method, and his academic achievements contributed to the development of early modern Japanology (Kokugaku) and became a landmark of the history of the study on the Japanese classics, thus greatly influencing the establishment of old kana orthography of the posterity.