Intriguing concept. Almost man in the iron mask scenario except the passenger has a lot more freedom.
We also assume that they are male considering the superstition on females on board ( I know that only applies to crew but still)
Maybe even a failed experiment I.e. The Invisible Fur...
One point did catch my attention. The dismissal of a crew man for accidentally saying hello instead of a reprimand.
Be curious where you take this.

I'd read this if you fleshed it out. I can only begin to speculate on the man's story. (If you hadn't invented the character McKennah I'd say this guy was the royal spymaster)

I think I have worked out his identity.. Willing to chat via notes :)

I'd love to hear it!