Kaisen Jōki served as a monk and priest in the Rinzai school of Buddhism associated with the Myōshin Temple in Kyōto during the Sengoku and Azuchi-Momoyama periods.
Born in 1502, Jōki may have originated from the Toki clan of Mino Province, entering the priesthood at the age of twelve. His mother died in the spring of 1545. Jōki observed the teachings of Jinshū Sōjū of the Myōshin Temple in Kyōto. After spending time at temples in Mino Province, Jōki became the forty-third leader of the Myōshin Temple, residing at the Sōfuku Temple in Mino. He left Mino temporarily after a religious rebellion known as the Eiroku betsuden no ran occurred in response to Saitō Yoshitatsu, the sengoku daimyō of Mino. Following the death of Yoshitatsu, Jōki returned to Mino.
In 1564, Jōki entered the Erin Temple upon invitation of Takeda Shingen, the shugo daimyō and sengoku daimyō of Kai Province. In his role as a priest, he served as an intermediary between the Takeda of Kai and the Saitō of Mino. Shingen awarded him the honorary name of Kizan.
In the autumn of 1565, Shingen’s eldest son, Takeda Yoshinobu, plotted a rebellion, but it was detected in advance, whereupon Yoshinobu was incarcerated in the Tōkō Temple in Kōfu. At this time, Jōki joined with Harukuni Kōshin of the Chōzen Temple and Aida Keisei of the Tōkō Temple in an effort to mediate a settlement between Shingen and Yoshinobu, but, in the autumn of 1567, Yoshinobu took his own life at the Tōkō Temple.
In the spring of 1573, Shingen died of illness at Komaba in the Ina Disrict of Shinano Province during a western campaign. The Takeda clan concealed Shingen’s death while his fourth son, Takeda Katsuyori, became its next leader. In the spring of 1576, Jōki served as the officiating priest while Katsuyori acted as the chief mourner at a memorial service for Shingen at the Eirin Temple in Kai.
In 1581, Jōki received the honorary title of daitsū-chishō kokushi from Emperor Ōgimachi.
In the spring of 1582, the Takeda clan was eliminated by Oda forces during the Kōshū Conquest (Kōshū seibatsu). Aida Keisei died in a fire at the Tōkō Temple in the conflict. As chaos enveloped the former territory of the Takeda, Jōki hid in the Eirin Temple certain individuals opposed to Nobunaga, including Sasaki Jirō (Rokkaku Yoshisada) and Yamato Awaji-no-kami, a retainer of Ashikaga Yoshiaki from the Jōfuku cloister at the Mii Temple, refusing to turn them over to Oda Nobutada. This was based on the societal precept during the middle ages that temples were sacred sites. Nevertheless, Oda forces proceeded to burn down the Eirin Temple during which Jōki and a significant number of monks died in the fire.