if you are creating a Beat'm Up game just one idea comes to my mind. I think you could create invisible boxes and append them to a fix point on the mesh, for example the hand. (like when attaching a weapon to a mesh, maybe as a subnode of the node) Then, because the box always moves with the mesh's hand, you could check for the collision between the invisible box and the invisible boxes on the other mesh (e.g. the head box).
The same principle is used in some shooters to check with part of the body is hit by the bullet.
I don't know how to attach something in irrlicht, but maybe it helps