[Well, he should have expected that. Ragna is about to try and think of something for them to do instead, when suddenly Mitsunari gets one of his terrible ideas that cannot possibly go well.]

You ain't getting one.

[He scowls. It's hard being a responsible adult, but he gets a feeling that if he doesn't persuade Mitsunari to abandon whatever he's planning it'll be a real pain in the ass later on.]

First, they're hella expensive. [He assumes, since those things usually cost an arm and a leg. Though to be fair, they could probably easily afford one with the amount of treasure they've accumulated over the years, which brings him to the next point.] Second, it's pointless on a ship. And third, you'd find some way to turn it into some kinda death machine. Hell, you'd probably have Motochika attach saws and flamethrowers to it or some shit.

[You can't convince him this isn't what Mitsunari is going after here. But Ragna isn't a monster and doesn't mean to deny him the joys of advanced technology, so he's willing to propose a solution that should satisfy both of them.]

... but if you promise you'll be a good boy we can do some window shopping.

[Look, this is the most he can trust him with.]