This chapter discusses the basic characteristics and historical formation of the combination of the deities Fudō Myōō 不動明王 (Skt. Acala[-nātha] Vidyārāja) and Aizen’ō 愛染王 (Skt. Rāgarāja) in Shingon 真言 esoteric Buddhism. In medieval Japan, various beliefs and practices were established in Shingon, in particular in the Ono 小野 branch of the tradition, which centred on these two deities. Their cult eventually came to constitute one of the most important elements marking the identity of Shingon esotericism, but little is known about how the Fudō-Aizen combination was initially formed. Traditionally, scholars have emphasized that the cult was created in Japan. The present chapter, however, aims to expand this view by looking at the issue from the standpoint of two different intersecting networks, a ‘translocal’ human network stretching between China and Japan and a ‘local’ conceptual network of ideas and practices developed in Shingon. In other words, it argues that the Fudō-Aizen combination became one of the hallmarks of medieval Shingon through the combined result of two factors, one being the translocal dissemination of Chinese esoteric Buddhist doctrines to Japan, and the other a specific, local ritual development within the Ono branch of Shingon.
Concretely, the chapter highlights two important clues to investigate the formation of the Fudō-Aizen combination in Shingon. The first clue is the composition of the ‘Aizen Mandala’ 愛染曼荼羅 said to have been brought to Japan from China by the Tendai 天台 monk Enchin 円珍 (814–891), but which circulated among both Tendai and Shingon circles in the medieval era. In this regard, it is argued that the notion of Fudō-Aizen must have been part of the knowledge of the Buddhist intellectual circles that produced the Aizen Mandala and that its origin might therefore ultimately lie in China. The second clue concerns the Rain Prayer Sutra ritual (Shōugyōhō 請雨経法), one of the earliest ritual practices of the Ono branch of Shingon which involved a meditation on Fudō and Aizen. With respect to this ritual it is shown that its structure was actually based on key notions found in the Yuqi jing 瑜祇経, an important Chinese scripture brought to Japan in the early ninth century. In this way, the chapter contends that the Fudō-Aizen cult was initially formed in Shingon as the result of integrating esoteric beliefs transmitted translocally from China to Japan into the local, conceptual network of rainmaking.