Sokushinbutsu (即身仏) are a kind of Buddhist mummy. In Japan, the term refers to the practice of Buddhist monks observing asceticism to the point of death and entering mummification while alive. Mummified monks are seen in a number of Buddhist countries. Only in Japan are they believed to have induced their own death by starvation.
There is a common suggestion that Shingon school founder Kukai brought this practice from Tang China as part of secret tantric practices he learned.
During the 20th century, Japanese scholars found very little evidence of self-starvation of Sokushinbutsu.
Emperor Meiji banned this practice in 1879, and assisted suicide—including religious suicide—is now illegal.
It says self-starvation and death by starvation.
So does it considered "Nirvana"?
What would Buddha's aspect of self-mummification be?