Object Local Y-Up being forced to be World Y-Up

I currently have a cube translating forward in its local Z while rotating towards another object. Code attached to cube:

 public GameObject cubeTarget;
 //Movement:
 transform.Translate(Vector3.forward* .1f,Space.Self);
 //Gives us a simple direction for the Quaternion look method
 Vector3 relativePos = cubeTarget.transform.position - transform.position;
 //Calc and apply:
 Quaternion rotation = Quaternion.LookRotation(relativePos);
        transform.localRotation = rotation;

This works almost as intended, but I believe the Quaternions are forcing the cube to have it's local Y up be world Y up. I would like the cube to follow the target object and be able to do a loop similar to a plane(which results in its local Y-up actually being World Y-Down) - but when tried in the scene it snaps violently back to Y-up.

I'm sure I'm missing some Euler calculations but I haven't been able to have any success with the functions I found in the docs.