It's cute on its own but I think it's much too small in scale for that space. If you'd like to do shelves, I would suggest a larger vertical rectangular piece with a few/several shelves.

You could either set it on the toilet, or hang right above the tank. You could roll up and tuck a couple of hand towels in there, or use it to hold an extra roll of TP, tissue box, or 'special freshener' Then hang a basic floating shelf above it or vs vs. that's the only way to use the cubby shelf , as it is too small for that space. Can you turn it at an angle? That's all i can suggest, other than get a larger shelf, maybe even a glass door cabinet.

You could also get 3 larger box shelves in a style similar to that and hang them vertically with some space in between them.

I actually really like the scale of the box for this space, but think it might be lonely on it's own. Can you buy 1 or 2 more in the same or similar size and stack vertically?? It seems like a great space for extra candles & perfumes!

You could get a piece of balsa wood at the craft store and cut it to the size of the inside of your box. Then glue or mod podge a pretty piece of scrapbook paper to it and put it inside the box. Whatever you put it in will stand out and keep it from just blending into your wall. If you want to show the X in back, just glue the paper to the back side of the box.