In Japanese the name given the priests of the Shugendo religion breaks down into yama, meaning mountain, and bushi (often mistranslated as warrior), meaning to lie down. Shugendo itself is unique to Japan, a blend of Buddhism, Shinto, and animism. The religion lives today, and remains strong enough to draw the faithful and tourist alike.
1400 years ago a prince named Hachiko came to the Three Mountains of Dewa (Haguro, Gassan, and Yudono), as the firstborn son of Emperor Sushun, Prince Hachiko's arrival would have drawn a great deal of attention. Hachiko abandoned his palatial comforts as the first step towards enlightenment. And just as Siddharta Gautama warded off the devils of temptation and lust under a bo tree in India, Hachiko too struggled with the demons of the ego. His battleground was the mountains of Yamagata, and as the founder of "Haguro Shugendo" Hachiko came to be revered as Gokaiso , the "Opener of the Mountains".
Thousands of yamabushi have followed Hachiko's example, immersing themselves in nature and severing all worldly connections, to purify their bodies and minds. In this way believers lose their individuality--burning away their egos with the hardships of hell--and are able to see through the world of delusion and be reborn as one with nature.
Thus by becoming an ascetic one essentially commits spiritual seppuku.