Reiku (1652 - November 4, 1739) was a Tendai Sect priest in the middle of the Edo period. His first name was Mitsunori. He called himself Gengen-an. He came from Fukuoka, Chikuzen Province.
At the age of 17 he became a priest at Enryaku-ji Temple on Mt Hiei, and then Inju (the chief of a temple) of Seiko-in in Saito (Western Section) on Mt. Hiei. At the age of 27 he became disciple to Myoritsu, and after Myoritsu's death in 1690, he, together with Myoritsu's disciples, worked hard to restore the style of the priest. By the middle of the Edo period, as Hongaku philosophy (philosophy of awareness) through oral instruction, which had started in the period of the Northern and Southern Courts (Japan), was becoming more prevalent, and Tendai doctrine and manners of priests had deteriorated markedly, he worked hard to correct the priestly ethic by reforming two types of learning, namely Jo (Samachi) and E (Wisdom), and introducing additional precept learning based on Shibunritsu (Four-Part Vinayapitaka, which explains about regulations and prohibited matters of the priests) in perceptive science. In 1693, he renewed Anraku-in in Sozan (literally, founder's mountain) Iimuro into Ritsu-in (vinaya temple) regarding additional precept learning based on Shibunritsu under the order of Cloistered Imperial Prince Rinojinomiya Koben and become the founder of the Anraku-in School.