Collaboration for peace with other religious communities has been a particular concern of the modern Japanese Buddhist lay organization Risshō Kōseikai since the mid-1960s, especially through its founding president Nikkyō Niwano (1906-1999). This study examines how and why this interreligious peace program developed, as well as its objectives and functions for Risshō Kōseikai. The Buddhist concept of purposeful adaptation shapes the development and content of the program. The ideas surrounding "peace through religion" are primarily influenced by socio-political ideals in Japan from the late Meiji period until the end of World War II. These ideals serve as a global model and leadership character for Risshō Kōseikai. In this context, the appeasement of the spirits of the war dead, neo-Confucian ethics, and the teachings and prophecies of the Lotus Sutra play a significant role.