A subsect of the esoteric Shingon school of Japanese Buddhism that is generally considered heterodox. The school formed in the early 12th century by combining Taoist yin-yang thought with Shingon ritual practice. It is so named because it was in the town of Tachikawa that the Shingon priest Ninkan is said to have transmitted esoteric teachings to a Taoist master, who then combined the two methods into a single school. Because of its actual use of ritual sex and accusations of involvement in black magic, the school was frowned upon and its leaders frequently sent into exile. The monk Yzūkai (1345–1416) is generally credited with extirpating the Tachikawa school from Shingon. See also Taoism.