Shinnyokai Shonin (1687–1783) was an ascetic monk of the Shingon Buddhist tradition associated with Mount Yudono in Yamagata Prefecture, Japan, revered as one of the sokushinbutsu, or self-mummified Buddhist practitioners. He undertook extreme austerities as part of the shugendo practice of Yudono lineage monks, culminating in a form of self-mummification believed by adherents to reflect a state of enlightenment attained through bodily discipline. His preserved remains are enshrined at Dainichi-bo Temple, where he continues to be venerated as a focus of memorial devotion and reflection on impermanence and the afterlife.