Kaishakunin - Wikipedia

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 and political activist Masakatsu Morita during their seppuku.