I guess he's just coming around to it
Between the MC being a pretty strong and well-known dude and the fact that everybody else on the ship is likely fucking him (which can even include the AI), I think he's realizing he's missing out
Viewing post in Lust Odyssey (NSFW Visual Novel) comments
I finally got Katari to have full sex and bottom for the mc/captain on that Sithyryan beach, it helps to have your mc/captain set be a dominant/top in the settings.
When you get to the beach in a drunken state Katari will resist bottoming and protest. But he will do it if you insist and not like it.
It becomes obvious Katari is frustrated due to being abused and dominated all his life, he can only truly assert a degree of power during sex which is why he often becomes aggressive sexually and doesn't like bottoming, for Katari bottoming is a form of being subjugated again.