Righty then.
If you look very carefully at certain
scenes in which Mikoto the cat herself is present, but
not in the actual shot itself, you will see a shadow vaguely resembling the human mikoto cast on the walls/trees/whatever is nearby.
Though compounding to the mystery of whether the cat is possessed by a human spirit is that
the cat and the shadow/supposed spirit are never in the same frame together, opening up the possibility that there just might be a completely human Mikoto sneaking around somewhere out there in the MO world...