Haha, alright, I was off by a hundred years. Still, a wizarding shogunate would be pretty cool, no? If not a single shogunate, a lot of daimyos would work... having a lot of warlords could be fun. My pre-shogunate Japanese history is fairly poor though.
Ok, what kind of government would Japan have then? There's no history of democracy pre-WWII. It's all military dictatorships and feudal style with the emperor as a figure head.