Sogen Kato was thought to have been Japan's oldest man until his mummified remains were found in 2010 (3). After analysis, it was found that Kato actually died in 1978 and that he was not the oldest man in Japan (1). Although not many details about Kato's life are publicly known, in 2010, his granddaughter claimed that Kato "shut himself in a room on the first floor of our home 32 years ago and we couldn't open the door from the outside" (1). Kato was found dressed in underwear and pajamas, with a blanked draped over him (4). The autopsy in Adachi was not able to determine the cause of death (1). Ultimately, fraud charges were filed against relatives of Kato for falsely claiming he was living (3).
Kato's relatives claim that he died practicing Sokushinbutsu (1). This Buddhist term refers the practice of observing austerity to the point of death (2). This is effectively a method of self-mummification (2).
After investigators forcibly entered Kato's room, an autopsy was conducted to determine the cause of death. However, due to the condition that the mummy was in, no definitive cause was found.
(1) Sogen Kato - https://en.wikipedia.org/wiki/Sogen_Kato
(2) Sokushinbutsu- https://en.wikipedia.org/wiki/Sokushinbutsu
(3) Fraud charges - http://www.bbc.com/news/world-asia-pacific-10809128
(4) Additional Details - http://www.independent.co.uk/news/world/asia/tokyos-oldest-man-died-30-years-ago-2039086.html