[The name sounds to Law like one someone might have in the country of Wano, but he's not dumb enough to think the countries in various worlds would line up so conveniently. In any case, after his hand is shook, he resolves that this guy can clearly see and is just like.... deeply odd? That's the easiest explanation. He refuses to keep being irritated by the ambiguity.]

That's good to know. [He considers Mamoru for another long moment, before deciding to try and set some standards here. The way the man asked about his own sword sure seems to indicate he normally had one, so.]

I'm a doctor, so if you ever get your own sword back and do something stupid, I might be available to put you back together.
[This is almost like an offer of friendship coming from this guy.]