Glasses
Watanuki has always been glad that he needs glasses to see.
When he was younger, he would take them off as often as he could. Without them, the world became beautifully dull and confusing; the things that dogged his every footstep became far too blurry for him to see. It was his small way of escaping.
Now, he is older and a tiny bit wiser. He rarely takes his glasses off. Now, the unknown was a more frightening thought that what he could see, and though he still hated seeing them, he at least knew what they were.
Still, he holds onto the childish notion that he can take them off whever he likes.