Sokushinbutsu(即身仏?) refers to a practice of Buddhist monks observing austerity to the point of death and mummification. This process of self-mummification was mainly practiced in Yamagata in Northern Japan between the 11th and 19th century, by members of the Japanese Vajrayana school of Buddhism called Shingon ("True Word"). The practitioners of sokushinbutsu did not view this practice as an act of suicide, but rather as a form of further enlightenment. Those who succeeded were revered, while those who failed were nevertheless respected for the effort.
It is believed that many hundreds of monks tried, but only 24 such mummifications have been discovered to date. There is a common suggestion that Shingon school founder Kukai brought this practice from TangChina as part of secret tantric practices he learned, and that were later lost in China.
Today, the practice is not advocated or practiced by any Buddhist sect, and is banned in Japan.
The practice was satirized in the story "The Destiny That Spanned Two Lifetimes" by Ueda Akinari, in which such a monk was found centuries later and resuscitated. The story appears in the collection Harusame Monogatari.
In January 2015 the 200 year old body of a mummified monk in lotus position was found in the Songinokhairkhan district of Ulaanbaatar in Mongolia. 
In the Megami Tensei games, a practitioner of Sokushinbutsu known as Daisoujou makes numerous appearances.
In the InuYasha series, a monk by the name of Saint Hakushin went through the process of Sokushinbutsu in times of famine and war in order to be able to protect his people forever as a living buddha. During the process he realizes the people outside are waiting for him to die and begins to resent them, allowing his undead mummifed body to be convinced to help the main villain with his vast sacred powers.
In Osamu Tezuka's Phoenix: Karma, Saruta's mentor commits suicide in this manner because he has been driven to despair by the government's misuse of Buddhism for political gain.
In the Anime and Manga Naruto, a being known as the Demonic Statue of the Outer Path has an appearance that is loosely based on this practice, looking somewhat like a mummified monk in the lotus position.
Hori, Ichiro (1962). "Self-Mummified Buddhas in Japan. An Aspect of the Shugen-Dô ("Mountain Asceticism") Sect". History of Religions1 (2): 222–242. doi:10.1086/462445. ISSN0018-2710. JSTOR1062053.|accessdate= requires |url= (help)
Hijikata, M. (1996). Nihon no Miira Butsu wo Tazunete. [Visiting Japanese Buddhist Mummies]. Tokyo: Shinbunsha.
Jeremiah, K. (2009). Corpses: Tales from the crypt. Kansai Time Out, 387, 8-10.