Sometimes creating a story's beginning can be very challenging. But who said that you have to start from the beginning? I tend to jump around and work on whatever parts interest me at that moment.
Okay, so you said you have two characters, and then what? Are you looking for an intro to a plot or the whole plot? You must have some ideas. So what about these two characters? Are they related ~ brother/sister, father/daughter, are they friends, strangers, what? Most rpgs include exploration. So think. What would cause these two characters to travel to a different town? Will this be a typical rpg or are you looking for something more unique? When is your story set? These are some things you should think about when creating your game.