Mickey "the Mailman" may very well be one of the - if not the - first support characters you will encounter in the game. However, he is one of the last to actually join up with you.
Mickey is kind, diligent and very reliable. He takes great pride in his job as a mailman, delivering mail to the all corners of the world. By doing so he has made friends everywhere. Once Mickey counts you as one of his friends as well, he will gladly offer you his services.
Because of the extensive knowledge he has accumulated from delivering mail to almost any location you can think of, he knows which routes are safe to travel and which aren't.
When you take him with you, the enemy encounter rate of most early game and mid game locations will be decreased to zero! This makes him a perfect companion for when you want to do some exploring or backtracking, but don't want to be bothered by enemies that you can beat with two hands on your back.