Classic Tomb Raider Aim Style

Good afternoon I am trying to replicate the style of aiming used by the classic tomb raider. It is clear that with an aim off set it is not possible to do this type of aiming so I will have to mix the rotation of the bones. I have drawn a line from the bone to the enemy to calculate the rotation it needs so that the arm is pointing at the enemy but there is no way to work … someone who can give me a hint please … thanks !!!