What is "kaishakunin"

A kaishakunin is an appointed second whose duty is to behead one who has committed seppuku, Japanese ritual suicide, at the moment of agony. The role played by the kaishakunin is called kaishaku (nin means person).

Aside from the purpose of being spared prolonged anguish until death, both the condemned and those on hand to observe are spared the spectacle of the writhing death throes that would ensue. The most recent kaishakunin of the 20th century was Hiroyasu Koga, who beheaded the novelist Yukio Mishima during Mishima's seppuku.