Blood feud

A Blood Feud
A blood feud is a deadly and often legal vendetta against another person. Almost any kind of offense can start a blood feud, but it usually is declared when a samurai dies needlessly at the hands of another. The victim (if he was dishonored or wronged rather than killed) and his immediate family are the only ones who may participate in the feud.

Declaring a Blood Feud
In order for a blood feud to be legal, written consent from the family's daimyo is required. After that, it is as though the family declared war on the offending party or parties. No one save for the Emperor may intervene unless they want to damage the feuding family's honor and encur their wrath as well.