Overlay color to edges of 2D object - material

I’m wanting to make a material that I can place over a sprite and in return the sprite will have a colored border.

The problem I’m experiencing is that my current material is covering only 3 of the four sides(square sprite) and that one side is thicker than the others. In addition the sprite disappears and only the border shows. I would like this material to border only the visible portions of whichever sprite it’s placed upon.

Tons of talented people here and no one has the slightest idea how to go about this? Can’t be post processing because it is a mobile game.