A Rinzai-sect Zen monk, poet and calligrapher, Isshi was born in Kyoto as the son of a court noble. At fourteen, he entered Shokokuji Temple in Kyoto, and in 1626 he moved to Nanshuji Temple in Osaka to study under Takuan Soho. When Takuan was exiled to the north in 1629, Isshi went with him and spent a year caring for his needs.
In part because of his noble background, Isshi had close ties with tea and calligraphy circles in Kyoto. His acquaintances included Karasumaru Mitsuhiro (1579-1638), Kobori Enshu (1597-1647) and Shokado Shojo (1584-1639).