Nagi smacks Owain's untrustworthy swordhand. Mostly to get it away from said hilt of the sword. No need for threatening gestures around here. Yes, he's taking Saber's advice a bit seriously, mostly because he knows how royal guards can be.

"Where we're going, you won't need that."

Nagi didn't have a worry either way. Most members of royalty had their pride invested in treated guests properly. Harming a guest was tantamount to harming your own people, which meant only the insane would do it. No, he had quite a bit of faith in this.