[@Diexsmiling] Awesome! A long-term quest or two is really great to have! An introductory problem, I think, would be something more immediate that he might need help with -- a situation he is in at this present moment that would be very difficult to get out of alone.

The other PCs should have the chance to build some trust with Hatori before they'll even let him aboard, let alone agree to help his quest. A smaller, maybe even mundane problem would help start that interaction. Maybe something having to do with a subject he's not very good at? What are his weaknesses?