Keep your hands off of others
While you should generally keep your hands off of others regardless of where you are on the planet, there are some instances where it’s okay. Take, for example, brushing someone’s shoulders off to remove snow, plucking a loose feather from the back of someone’s coat, or giving a buddy a slight pat on the back.
But in Japan, unless you’re literally saving a life or in a romantic relationship (never in public), you should keep your hands to yourself at all times. That’s just the way things are over there. Even if you want to seem friendly, there are others way you can do so without touching someone.