Mukotsu was a member of the Band of Seven, a group of merciless bandits who were resurrected by Naraku. He specialized in using all kinds of dangerous poisons (which seemed to only work on humans). Despite his crafty nature, he was incredibly insecure about the ugliness of his face, which he said made all women hate him. He was killed by Sesshomaru simply because he got in Sesshomaru's way.