Julian:
Firstly, nice sword. As far as it belonging to a general, it's hard to say. The tassel that is on the sword, if original, is not the type that would be on a general's sword. Secondly, and more importantly, as to returning the sword to the family: this would be problematic for several reasons. As a military sword (assuming the blade was made during the Showa era), you most likely would not be allowed to bring the sword into the country. There are some extremely strict rules regarding swords and registration in Japan. Additionally, many Japanese families would rather not have a "war" reminder of their relatives. This is of course a generalization, however it is often true.
My suggestion would be to continue having fun doing the research and the discovery but not worry about returning it.
Regards,
John C.