>>48212
It seems like it was handmade, as they say it looked like it was wrapped in tape but also it had two barrels. It looked like there was a lot of smoke as well, too much to have come from a normal firearm, like it might have been black powder. So maybe it was just two metal tubes filled with black powder and ball bearings and using some kind of ignition mechanism.

It's very odd, but then Japan is like that sometimes. It says the guy used to be in the Navy so maybe there were ultranationalists motives.