Ginkotsu is Renkotsu's assumed best friend, since the two are hardly ever apart. Renkotsu built Ginkotsu's mechanical body and kept it running throughout the time that Ginkotsu had it before it was blown up by Inuyasha. Renkotsu then rebuilt Ginkotsu's tank body in a cave with a whole new variety of weapons, making Ginkotsu a walking arsenal. (Source: Inuyasha Wikia)