It wasn’t what I imagined, so I want to return it.

You cannot return an item simply for personal reasons. In Japan, once you buy something from a store, returns are not accepted unless the item is defective or the staff gave you an incorrect explanation when you bought it, or in special cases. So even if the item you bought wasn’t what you imagined, that is not a good enough reason. You won’t get a refund. On the other hand, some stores may accept returns under certain conditions. Check with the store before making your purchase.