There's no
Futa/Trans Protagonist in the tags, just
Futa/Trans and there's indeed a Futa/Herm character in the game at the moment.
Strive for Power allows you to fiddle with the rules and spawn nothing but female characters and you create your own character; female, male or futanari. Most interactions are text based however, with a handful of images for key characters. Probably one of the more in-depth games out there featuring futanari characters, together with
Trials In Tainted Space, also text based however.
Other examples
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Strumpets, very slow on updates however and you've far less control over who to sexually engage with. Haven't played it since forever, so things might have changed
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Venture Seas, allows you to play female, male and futanari. I think you've near complete control over who you sexually engage with. Slow updates, quite buggy last time I played it and it's a slow burner due to how the combat and exploration mechanics work.
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Futanari Quest, probably the most hated game on the site, haven't tried the "full release" of the game. But, you're a futa and you'll encounter a handful of female NPCs.
There's more, just use the
Latest Update feature and enter the tags you're looking for. It's not optimal, seeing how some tags are missing from some games, but it should get you started.