This paper addresses the relationship between Zen and tantric or esoteric Buddhism in premodern Japan from the point of view of the Buddhas and Buddha bodies considered to be preaching these two traditions. After surveying theories on the dharmakāya teaching already present in Chinese Buddhism, it considers the development of this doctrinal notion in the Japanese tantric traditions. The paper demonstrates that this tantric discourse on the Buddha as preacher provided thinkers such as Enni 圓爾 (1202–1280) and Chikotsu Daie 癡兀大慧 (1229–1312) with a framework to integrate Zen into a tantric world. Eventually, and under the influence of embryological motifs circulating widely in medieval Buddhism, Zen practitioners came to establish their own theories on the human as Buddha body. The paper concludes that medieval Zen and medieval tantric Buddhism should be considered sister movements.