There's also Jerynn in the bar on Uveto, who eventually puts a collar on you if you blackout from the cold in middle cold Uveto outdoors, and she has an optional Bad (read: Good) End if you do it enough. Lund in Korg'ii Hold, also on Uveto, has some stuff where you become his pet/slave. Urbolg on Zheng Shi, the latest planet, has a couple of scenes with a collar where you quickly become his toy and get a Good End. I think the boss, Overseer Maike, has some slave stuff, but I haven't tried it. Akane, whose unlocking is a bit involved, has S&M content where she restrains you and makes you scream. On Myrellion, in the Gold territory (Kressia?) there's also a chance that you'll be kidnapped by Gold Myrs and forced to satisfy a ton of them against your own wishes.
Then there's a bunch of Ends where you become someone's sex slave or such if you lose enough, like the Wetraxxel Brawler on Myrellion, the Milodan Male on Uveto, but they aren't really repeatable without saving and loading a lot.