Seijun (year of birth unknown - May 2, 1566) was a nun of the Rinzaishu sect in the Sengoku Period (Period of Warring States). She devoted herself to restore Shikinensengu (periodical rebuilding of a shrine carried out every predetermined number of years) of Ise-jingu Shrine. The third chief priest of Keiko-in Temple.
Seijun is said to be from Kumano County, Kii Province or from Omi Province. Seijun became a disciple of the second Hozan Chikei (宝山智珪) of Keiko-in Temple which was later handed over to her. In 1549, Seijun went on a pilgrimage to various districts and successfully solicited funds for rebuilding of Uji-bashi Bridge (Ise City) over the Isuzu-gawa River. Having heard the news, Emperor Gonara gave Seijun the title of Shonin (high priest) in particular and conferred the title of 'Keikoin' to her monastery. Later, Seijun made her pilgrimage to various districts again as a Kanjin bikuni (nun soliciting funds) for the Shikinensengu restoration of the Ise-jingu Shrine, which had been suspended for more than 100 years, and she first realized the transfer of Toyouke Dai-jingu Shrine for rebuilding in 1563. She then planned temple solicitation for the transfer of Kotai-jingu Shrine but died from an illness shortly. Later, the simultaneous Jingu Shikinensengu (rebuilding of the inner and outer shrines of the Ise-jingu Shrine) was realized by its disciples in 1585.