A sokushinbutsu (即身仏, "そくしんぶつ") was the mummified body of monks who wished to attain enlightenment by becoming a living Buddha. They would abstain from eating until they died. They would meditate during that time while being surrounded by candles in order to dry their body faster. The final step before becoming a sokushinbutsu was for the monk to be encased in an underground tomb. It would only be large enough to allow them to sit in the lotus position. They would ring a bell connected to the outside so their followers would know if they were still living or not. There was a tube that allowed air into the underground tomb. Over 100 years before Inuyasha had awoken from his spell, Saint Hakushin mummified his body in order to save the people from famine and pestilence in the region.
- Sokushinbutsu on Wikipedia