The impression I got from the OP was that the CHA checks were related/directed to the Mad Tyrant, so we're getting even more counterfactual here by having it aimed at the Captain; but I'll play this game for the nonce. If the Captain is so much the focus of the Mad Tyrant's Bond, he seems as though he might need fleshing out the same way as the Mad Tyrant, and he needs to be the sort who'd earn the Mad Tyrant's trust, keep it, and not act out before now. It's at least as easy to write those so his Bond is, e.g., "An insult to my Lord is an insult to me" as anything else; maybe his Ideal is "I will do what I must to keep the peace between my Lord and the citizens" and his Flaw is "I keep my Lord's trust by keeping my silence." Now we have an NPC who'd be the sort of quiet sideman who'd be the focus of the Mad Tyrant's Bond, and keep his position and other wise fit into the setting as described. And by insulting the Mad Tyrant, the PCs have triggers the Captain's Bond, and made it much harder for them to persuade him not to arrest them.