Kukai: Japan's First Vajrayana Visionary is a wide-ranging account of how the ninth-century founder of the Japanese Shingon school of Buddhism, Kukai (774-835), effectively forged a unique identity for the new meditative and ritual practices he learned during two years' study in China. While esoteric ("tantric") Buddhism is also known as Vajrayana ("vehicle of the diamond/thunderbolt"), Kukai alternatively named it the "esoteric teaching" (mikkyo), Vajrayana, and Shingon, the Sino-Japanese term for "mantra." He carefully articulated how contemplative practices engaging the "three secrets" of body (symbolic gestures, mudra), speech (recitation of mantra), and mind (visualizing the world as a mandala) radically transform one's sense of self. These practices aim to uncover hidden dimensions of being to reveal a state of profound existential freedom and power that is an embodied manifestation of awakened consciousness. Kukai employed every available social and material resource to establish Vajrayana practices on a solid foundation.

This work examines his rigorous clarification of the distinctive character of Vajrayana practice that creatively portrayed it as taking goal of the path (Buddhahood) to be both its end and its means, and his forceful characterization of Shingon as the only form of Buddhism in Japan to enable the immediate accessibility of enlightenment. Kukai's extensive knowledge of canonical Buddhist texts allowed him to frame Vajrayana practice as a method that could unite the "two truths" (ultimate and conventional) via a multi-layered contemplative practice that expresses their fundamental unity. He affirmed the possibility of achieving enlightenment in "this lifetime" by revealing how "this body" is already intrinsically grounded in the qualities of a Buddha. The practices facilitate a thoroughgoing realization of this identity.

The book also details Kukai's engagement with debates active in China and India on the relationship between levels of embodiment (kaya in Sanskrit) understood to be possessed by a Buddha, and demonstrates the affinity his interpretation of Vajrayana has with later Indian and Tibetan models. It explores his rhetorical positioning vis-a-vis other Buddhist schools in Japan and highlights his ardor and urgency for promoting his vision of the power and beauty of Shingon practice.