These would be my recommendations:
No-Escape focuses primarily on bondage, heavily influenced by themes of sexual training and mind control. Although it also touches on a variety of other kinks.
Practically every enemy has a bad ending with a different kink and not all bad ends are no-cons or due to losing battles, there are quite a few that are due to (voluntary) decisions or actions of the player, especially the bosses have a negotiation phase where the protagonist can undergo training in exchange for avoiding a fight (which can lead to bad endings) if performed very well or very poorly.
Normally each boss (and some normal mobs) has two routes: Fight or Negotiate (usually training or serving the boss for a while before continuing the mission) and most bad ends have two routes to choose from, Voluntary/Slut (Pink) or No-Con (Red)
3072 ad is the game I'm playing now. It's not exactly 5* quality, especially the art, but I think it's pretty much what you're looking for. Every time you lose to a boss, they subject you to sexual abuse (training), and if you lose repeatedly, you can eventually give up and complete the sexual training. From that point on, you continue playing the game as a slave.
Two routes: warrior or slut
Secretary This game focuses primarily on the protagonist's training as a sissy secretary and includes a wealth of content, including hypnosis, mind control, and corruption. There's also plenty of content like latex maids, chastity, bondage, and more. It's quite comprehensive, but I only recommend it because right from the start, you have the option to transform from male to female (with a pussy), avoiding the sissy protagonist theme.
There are tons of decisions, most of them voluntary, though you can find the path you're forced to take (but overall it's highly customizable and you can decide on a game-by-game basis).
