Kukai died, by the traditional account, in the third lunar month of 835, though Shingon does not describe his death as an ordinary one. Adherents hold that Kukai entered a state of deep meditative absorption, nyujo, rather than dying in the conventional sense, and that his body remains seated in that state inside his mausoleum at Okunoin, at the eastern end of the mountain, awaiting the far future arrival of Miroku, the bodhisattva known elsewhere as Maitreya, who is expected to become the next Buddha. Monks at Okunoin still bring ritual meals to the mausoleum each day, a practice the temple describes as unbroken since Kukai's own time.
The approach to the mausoleum runs for roughly two kilometers through Japan's largest cemetery, a forest of well over a hundred thousand grave markers and memorial stones, many raised by noble families, feudal lords and companies wishing their dead, or their commemorative markers, to lie near Kukai in anticipation of Miroku's arrival. Koyasan was closed to women, along with several other mountains held sacred by Shingon and Tendai Buddhism, until the prohibition was lifted in 1872 during the Meiji era's reordering of religious law. The mountain, together with the pilgrimage routes connecting it to Yoshino, Omine and the Kumano shrines, was inscribed on UNESCO's World Heritage List in 2004 as the Sacred Sites and Pilgrimage Routes in the Kii Mountain Range, and its temples, more than a hundred of them, still host pilgrims and overnight visitors in guest lodgings attached to the monasteries.