How to forbid an NPC to move diagonally using Character Controller?

My game doesn't allow human players to move diagonally when played by 2 players. I started implementing the AI for when its only one player playing and so I need the computer to control the other player. Everything works perfectly fine except that it moves diagonally, which I dont want it to, and even though I have tried many things, they haven't worked. Any ideas?

This is how human player characters are forbidden to move diagonally:

// Simple character controller movement with the keyboard. function keyboardMove() { var toTarget : Vector3 = new Vector3(); if (p1) { if (Input.GetAxisRaw("P1Vertical")) { toTarget.z = Input.GetAxis("P1Vertical"); controller.Move(toTarget * Time.deltaTime * speed); } else if (Input.GetAxisRaw("P1Horizontal")) { toTarget.x = Input.GetAxis("P1Horizontal"); controller.Move(toTarget * Time.deltaTime * speed); } } else if (p2) { if (Input.GetAxisRaw("P2Vertical")) { toTarget.z = Input.GetAxis("P2Vertical"); controller.Move(toTarget * Time.deltaTime * speed); } else if (Input.GetAxisRaw("P2Horizontal")) { toTarget.x = Input.GetAxis("P2Horizontal"); controller.Move(toTarget * Time.deltaTime * speed); } }

 if (toTarget.magnitude != 0) {
     transform.rotation = Quaternion.LookRotation(toTarget);
 }

}

And this is how the NPC keeps moving the way it wants...

function move(aTarget : Transform) {
    var toTarget : Vector3 = new Vector3();
    toTarget.x = aTarget.transform.position.x - transform.position.x;
    toTarget.y = 0;
    toTarget.z = aTarget.transform.position.z - transform.position.z;
    if(toTarget.magnitude <= 0.2) {
        reactToState(state);
        return;
    }
    toTarget.Normalize();
    controller.Move(toTarget * Time.deltaTime * speed);
    if (toTarget.magnitude != 0) {
        transform.rotation = Quaternion.LookRotation(toTarget);
    }
}

Even if I don't find the answers I'm pretty sure these are 2 useful (part of) scripts anyone can use! :)