[@Mokley] Alrighty, I think I understand. As for his biggest weakness, I would say that his heavy reliance on martial arts and blades leaves him very vulnerable against ranged opponents. Also, his bushido and code of honor means that he really only agrees to fair fights, granting less honorable brigands and bandits an advantage since they aren't afraid to fight dirty. A lot of people also could fairly easily take advantage of his kindness and goodwill. 

I could think of plenty of situations he couldn't handle alone that would afford the opportunity to build trust with the other PCS before they officially band together. Getting stuck in a trap infested ruin, for one. Or maybe he could have just set off on an expedition that was too long and ran out of food and other supplies. 

As for help on his main quest, this could be a you scratch my back, I'll scratch yours sort of thing. For example, after he meets the other PCs and they help him out of a sticky situation, he could agree to help them with their journey in return for a promise to eventually come back to his home and help him overthrow the emperor. 

That was what I had in mind anyway, not sure if that's where you were going with this. Let me know what you think haha.

[@Sisyphus] Also, just want to mention that the posts so far have been [i]awesome[/i], really enjoying this story and I can't wait to get in on it xD