Shingon tradition holds that Kukai did not die in the ordinary sense but entered a state of eternal meditation, nyujo, within his mausoleum on Mount Koya, where he is believed to remain in a state awaiting the future Buddha Maitreya, at which point he will assist in that Buddha's teaching. This belief is a devotional development that took shape over the centuries following his actual death and continues to shape practice at Mount Koya today, where temple attendants still bring daily meal offerings to his mausoleum as an ongoing ritual observance rather than a historical reenactment, treating him as present rather than deceased. This devotional framework sits alongside, rather than replacing, the considerable historically documented record of Kukai's life as a scholar, engineer, and founder of the Shingon school, including his study in Tang China and his role in bringing Esoteric Buddhist teaching and ritual back to Japan, material that rests on firmer historical footing than the nyujo belief itself.
Separating the two is not a matter of dismissing the tradition's claim so much as recognizing it as a distinct kind of statement, a matter of ongoing religious devotion and doctrine about Kukai's continued spiritual presence, standing apart from the historical record of his documented career and its considerable, independently verifiable influence on Japanese Buddhism.