Rocketbilly Redcadillac, "Billy" for short (called "RB" by Juji), is the 17 year old ghost haunting an electric guitar that Juji found during his travels.
Juji's partner, "Billy" is a ghost haunting an electric guitar. Unlike Juji, Billy is a laid back ladies man, though bizarre enough, he considers his own grandmother to be the ideal woman. In combat, he employs the same guitar he haunts, using the dynamo attached onto it to deliver lightning strikes as he plays.
Billy excels at long range combat, quickly clearing rooms of henchmen with arcs of electricity. His melee skills are sub-par compared to his comrades, but he can charge his electric guitar to deliver powerful shocks.
He bears a passing resemblance to Vash the Stampede, of Nightow's earlier work Trigun.
It is hinted in Gungrave: Overdose that he used to be a World renowned rock-star, and was killed on stage mid preformance