Oh, so it was a shotgun. I guess I wasn't looking at it properly. That actually makes it better for Kazu & gang, since Shiba can't be sniping from far away. Although that being said, from a close distance shotgun is more troublesome, but at least Kazu & Co have plenty of close combat powers themselves, unlike long distance.
There really aren't many ways to deal with the likes of Shiba. Charles Bronson's way is pretty much the only one. Shiba was a violent tyrant even before this whole orc invasion thing, so he's even more so now. He's also personally responsible for deaths of humans already, so there's essentially no way back for him either, not that he would want it otherwise. They couldn't trust a single promise out of his mouth. If they leave him be, he will be back for more, which would be insufferable: they have already more than enough worries with the constant orc waves, so needing to worry about other humans attacking as well would be too much.