I remember seeing a feat or familiar archetype that allowed the familiar to transform into an item that could be magically enhanced (like a regular magic item) and I even created a character using this idea, but now I can't remember what Pathfinder resource I found it in. I know there is a similar dynamic in D&D but I'm looking for the pathfinder one.
Only thing that comes to mind for me is one of the powers that Mythic Archmages can get from Mythic Origins.