second in seppuku; kaishakunin
Historical term for the person who beheads a samurai performing seppuku to end the ritual. Often translated as 'second' or 'kaishakunin'.
See also: 介錯
The kaishakunin is responsible for beheading the person performing seppuku.
Rare modern extension; used for someone who assists or helps, often in a supportive role. Less common than the historical sense.
He organized the materials as an assistant for the project.