Help with rendering a model on top of the player

Hello. I really need help. II am making a mod where I want to make a custom animation for the player, but the player also has a seperate model attached to them. I dont really know how to explain it but I am trying to make a HxH mod and I want to make animations for all of the abilities. So I want to make the Jajanken ability and I want to make an animation where he uses his Jajaken. I just want the Jajaken to be a model, not a block or item or anything, purely visual. plsss help. Ill try to explain better if u dont understand.