I am also curious on how narrow this can be - I have a Japanese history textbook on hand here so can toss out a few ideas... But have no idea if they`d be too narrow. Really, the options are limitless.
Is there any specific period you`d like to limit this to? I can make a list up of the topics covered in the book but there is no way I`m doing it for prehistory to WWII.
A vague one that pops to mind, as I just watched a documentary on it the other night - The acceptance of women into 石山寺. But as it`s a topic getting it`s own documentary it`s probably already taken.