A kaishakunin (Japanese: 介錯人) 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 and political activist Masakatsu Morita during their seppuku.
Still preserved in modern-day movements (kata) of the martial art, iaido, the ritual of performing kaishaku varies very little between Japanese fencing schools, but all of them are bound to the following steps to be performed by the kaishakunin:
After the dead samurai falls, the kaishakunin, with the same slow, silent style used when unsheathing the katana, shakes the blood off the blade (a movement called chiburi) and returns the katana to the scabbard (a movement called noto), while kneeling towards the fellow samurai's dead body. When this is completed, the kaishakunin remains kneeling for a while, as a sign of deep respect to the fallen samurai who committed the ritual suicide, always in a state of "total awareness" (zanshin) before standing up and bowing (rei) to his body.
In some seppuku rituals, no disembowelment occurs. The condemned person merely moves the dagger, or, sometimes, a wooden stick or fan, across his stomach, followed by a beheading by the kaishakunin. In this variation, the kaishakunin becomes in effect the executioner, and seppuku becomes effectively a beheading.