Shinzei (800 - March 25, 860) was a Shingon Sect Buddhist monk who lived during the first part of the Heian period. His father was Junsatsu Danjo (official who patrols and surveys land) KI no Misono. He is also known as Takao no Sojo, Ki no Sojo and Kakinomoto no Sojo. His secular name is reputed to have been KI no Matsunaga. Although a monk, he was granted the kabane (hereditary title) of KI no Ason.
His talent was discovered by Kukai which led to him becoming Ajari (high priest) at the exceptionally young age of 24 in the year 824. In the year 836, he attempted to travel to Tang Dynasty China with Shinzen but failed and confined himself to Takaosan-ji Temple for the following 12 years where he practiced ascetism. During this period, he was appointed one of the naikubu-juzenshi (the ten priests selected for Buddhist services in the imperial court), betto (administrator) of Jingo-ji Temple, Gon Risshi (generally in Shingon sect, fifteenth-ranking Buddhist priest, literally, "supernumerary master of discipline") and second abbot of To-ji Temple. Shinzei was offered the rank of Sojo (high-ranking Buddhist priest) in the year 856 but he declined and his master Kukai was posthumously granted the rank of Daisojo (highest rank of the Buddhist priesthood). He passed away aged 61 in the year 860 and was buried at Shokozan Daiko-in Temple.