Renkotsu (煉骨, "Refined Metal Skill") was a killer who was also a member of the Shichinintai. An expert military engineer, he created explosives and incendiary devices, including a type of flaming oil that he could spew from his mouth. He also reconstructed Ginkotsu into a living artillery weapon resembling a modern tank. He was also a gifted strategist and had some skill at hand to hand combat, although the only members of the group he surpassed in fighting skills were Mukotsu and Kyōkotsu. One of the most dangerous members of the Band of Seven, Renkotsu was second in command after Bankotsu.