Most people in this 13 millions person city do thing's in groups. Wearing masks I guess is one of them.
So the sharp eye will notice that the book is not covered nor is the regular shape of a Japanese novel. The guy reads English! It's the little thing's like this that make the train journey interesting (for the most part).
Sometimes you point your camera in a direction and just hope something will fall into the frame. You don't expect to feel like your about to get killed (in Tokyo anyway) in the process. This could have been one of these times :-)