Yes, you can also return your own Z/X to hand since it does not specify any particular Z/X.
Z/X that can be returned are your own or opponent's Z/X in Normal Square, you can choose several Z/X if the total Cost of the Z/X that would be returned equal to 6 or less.
Case 1. 1 opponent's Cost 5 Z/X
Case 2. 1 of your own Cost 2 Z/X, 1 opponent's Cost 4 Z/X
Case 3. 1 of your own Cost 3 Z/X, 1 opponent's Cost 2 Z/X
Case 4. 3 opponent's Cost 2 Z/X