The relationship between Confucianism and Buddhism in East Asia has vacillated between conflict and mutual tolerance. In the late Tokugawa era in Japan, Confucian polemics against Buddhism became increasingly frequent and intense. This article investigates a representative example of the antagonism that characterized the late Tokugawa intellectual world: the book Zenkai ichiran (One wave in the Zen sea) by Imakita Kosen, a Rinzai Zen master, and the response it evoked from Higashi Takusha, a follower of Wang Yang-ming. The political factors of the time are also examined in order to clarify the background of this particular instance of religious conflict.