The Diamond appears after defeating The Spade and is the 2nd boss you face in Area 2. He is another one of The Joker's guards. As Namiko and your character arrive at the scene, The Diamond makes all the cars of the Heart Beats disappear. Jun The Angelic demands for his car to be returned but The Diamond offers to return them if your character defeats him.
He drives a Solar Red Toyota 2000GT MF10