When we seek the origin of consciousness outside brain activity, based on a physical viewpoint, the multi-dimensional universe picture is found to solve many difficult and non-trivial problems. Easy application of such a picture, however, causes a kind of hierarchy problem. The parasite fermion (PF) is the material particle that resides in the extra-dimensional space, namely outside the 4-dimensional space-time in which we live. Differences in the nature of the PF, together with the mechanism that causes the difference, from that of the material particle that exists inside our universe, called the host fermion, are discussed. The PF can be invisible due to the mechanism. What would the outcome be like, if we applied this novel existence scheme of material into the mind-body problem? Problems which need to be solved when we seek the origin of consciousness outside the brain can be solved by the PF model.