Translating parts in relevance to the position and rotation of another one?

Lets say I have two parts: The independent, or reference part, and the dependent, or translated part. If I were to rotate the independent, then the dependent would maintain its initial orientation in the perspective of the independent. An example would be a mirror. If you were parallel to a mirror, you would see yourself in the mirror. If you were perpendicular to a mirror, however, you would not be able to see yourself. How would I position the dependent so that if you were to gaze into the mirror at it's position, you'd always be able to see yourself? Also, imagine that the surface of the mirror was the top surface of the independent. I've given this past attempts and came close, though I lost my data and I'm not too experienced with CFrames.

You can find a visual for my question here.