 What distinguishes Kūkai’s understanding of the Buddha is that he takes the notion of the “embodiment of the Dharma” literally and radically. Hosshin in Shingon thought is not an abstract truth transcending the mundane world. Rather all phenomena and thing-events of this cosmos, in their very transience, are each themselves embodiments of truth and the cosmos as a whole comprised of these impermanent and interdependent beings is eternally an embodiment of truth, the hosshin. Moreover this concrete cosmic identification between Buddha, truth, and the cosmos of thing-events, was “personal.” That is, hosshin was equated with the Buddha Dainichi. The cosmos as the manifestation of truth, the Dharma, was itself hence equated with the body of the personal Buddha Dainichi. And in turn, Dainichi with his cosmic body is then the embodied personification of the universal Buddha-nature inherent in all beings and the Dharma that is manifest everywhere. Prior to Hui-kuo, this identification of Dainichi with the hosshin in Mantrayāna Buddhism was ambiguous and not thorough. In the Dainichi-kyō, a sun metaphor is used to name its central Buddha, “Dainichi” (Mahāvairocana, transliterated as Makabirushana), meaning “Great Sun,” as the being whose light illuminates and enlightens all beings in a way akin to the sun’s life-giving light. All other deities are seen as manifestations of this light. Dainichi’s identification with the hosshin nevertheless remains ambiguous. While he probably influenced Kūkai in regards to this equation, Hui-kuo himself however left no written explications. Kūkai thus has been regarded as the first to provide a complete and systematic exposition of the nature of the Buddha Dainichi as the hosshin. The sun metaphor of illumination – as the source of both being and of knowledge (enlightenment) – befits the universality of the hosshin perfectly. The illumination of the “Great Sun” (Dainichi) becomes accordingly understood to mean the omnipresencing of the Dharma throughout the cosmos, an omnipresencing in turn equated with the Buddha’s preaching. This “proof” that the hosshin does in fact preach helped Kūkai in distinguishing his esoteric doctrines from those of exoteric Buddhism.