There are more than 10 Buddhists in Japan who attained Buddha hood while still in the alive, and they are called Sokushinbutsu (即身仏). Sokushin is one of Buddha training ways to save people, take fears away and grant their desires by being a Sokushinbutu.
To put how to be a Sokushinbutsu concretely, one stops to have the five grains, and have walnuts, hazelnuts, and nutmegs instead which take away moisture and fat in the body. Next, the one is buried in a pit, and s/he recites sutra with ringing a bell. When the bell ringing stop can be heard from a hollow bamboo utensil connecting ground and the pit as an air vent: means the one died, dig up it, fix the shape, and burry it again. After 3 years and 3 months, it is dug up and to be seen and prayed for people.
You can still visit and see Sokushinbutsu as a complete mummy. Expressly, Yamagata prefecture has 8 Sokushinbutsu. I saw two Sokushinbutsu at Kaikouji(海向寺) in Sakata city, Yamagata. One is Chuukaishounin(忠海上人) who was born in Tsuruoka city, Yamagata. He became Sokushinbutsu in 1755 at 58 years old. The another one is called Enmyoukaishounin(円明海上人), turned to a Sokushinbutsu in 1822 at 55 years old.
The two Sokushinbutsu looked really mummy. I felt it was kind of scary when I saw them first time. They looked have hard skin like wood. The staff there explained about Sokushinbutsu things and sell original charms. Popular ones are red charm which include a piece of clothe that Sokushinbutsu wear. They wear red clothe in the shrine and the clothe are to be changed every 12 years. So, worn clothe are cut in small pieces and put them into charms.
Sokushin cannot be in modern life because most people don’t’ have need of food or things in Japan. However, when people had hard time they cannot eat and not satisfied lives in old times, priests commit suicide by throwing themselves into Sokushinbutsu to undertake all fears people have. They lost their lives by themselves, but that could be the only gratification to meet people and be prayed by them after hundreds and thousands years.