- Birth: 1543
- Death: 1592
- Other names: Honganji Kennyo, Kennyo Shônin
- Son: Kennyo Koju
- Distinction: Honganji leader
Kosa was the son of Shonyo Kokyô, the leader of the Shinshû Buddhist sect, who passed away in 1554. Leadership of the Ishiyama Honganji (Hongan Temple) and Kaga province passed to Kosa despite his youth with Imperial sanction. In 1568 Oda Nobunaga entered Kyoto, and relations between the Oda and Honganji quickly soured. In 1570 Nobunaga attacked the Honganji, which had become a fortress well stocked with provisions and firearms. Nobunaga's early attempts at a direct assault were repulsed, and he afterwards turned to reducing the Honganji's satellite forts. Kosa in turn called upon the assistance of the Môri family, who began ferrying in supplies with their powerful Inland Sea navy. The Môri navy was defeated in 1578 and the Honganji finally isolated. The siege nonetheless continued into 1580. Finally, in the 7th month of that year, Kosa agreed to surrender after the court's efforts to facilitate a peace. Nobunaga, in a rare show of temperance, accepted the offer. The Ishiyama Honganji complex was to be abandoned but the defenders were given pardon and the Honganji's temples in Kaga, seized by the Oda in the conquest of that province, were to be returned. Toyotomi Hideyoshi was to make use of Kosa's influence, and dispatched him to Kyushu to rally his supporters there in expectation of Hideyoshi's invasion of that island in 1587. In 1591 Hideyoshi permitted Kosa to build a new Honganji facility in Kyoto, which was constructed on three blocks in the southern part of the city.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005