The Ishiyama Honganji Presumed Site at Osaka Castle occupies an important place in Japanese history. The Ishiyama Honganji Temple, which was built as the base of the Honganji sect of the Jodo Shinshu sect, once existed on this site. In addition to being a religious center, Honganji also served as a strategic military point during the Warring States Period and was the scene of many historical events. Ishiyama Honganji was built in the late 15th century. This site was located in Settsu Province at that time, and was an important place for transportation and defense due to its geographical characteristics near rivers and the sea. In particular, Honganji was known for its role in the siege of Nobunaga and its fierce confrontation with the forces of Oda Nobunaga. The conflict between Nobunaga and Honganji lasted more than 10 years and is etched in history as the so-called “Ishiyama War. In the late 1570s, pushed by Nobunaga's overwhelming military power, Ishiyama Honganji finally chose the path of reconciliation. Then, in 1580, the site was burned to the ground after Honganji's head priest, Kennyo, left the temple. Later, Toyotomi Hideyoshi built Osaka Castle on the site of the ruined Honganji Temple, and the castle town was developed. Today, there are few traces of the former prosperity left at the site of the presumed Ishiyama Honganji Temple. However, this site not only played an important role in the formation of the city of Osaka, but also symbolized the intersection of religion and politics during the Warring States period. For this reason, the history of Ishiyama Honganji Temple and the subsequent development of Osaka Castle remains a topic of great interest to many people today.