At certain period of time in the Shogunate, fighters in the battlefield would have nothing personal against each other, but fighting in name of a different master. This led to a convoluted type of trade in the course of sword fights: the defeated could keep his head attached to his neck... as long as he paid the right price for it. If the defeated didnt have enough money to buy his own life, he would write a promissory and seal it with his own blood.
Hanshiro, a Kubidai Hikiukenin (or Promissory Taker, on free translation), is one of the many men that charged himself into making sure the promissories made at the end of a battle were fulfilled... either with money or blood.