A dominant lesbian, maybe with martial arts, magic or super powers with the desire to turn straight milfs (may include her mother) lesbian. Ideally in a steampunk or cyberpunk setting. Her physical prowess may be visible, but not in exaggerated way, some muscles are fine, but no steroids please and still a lot of curves. Dress the protagonist in black leathers, while her milf harem dresses more in a silk and lace style. So far, my perfect protagonist.
In more general terms:
I favor lesbian games, therefore I favor female protagonists. I prefer games, where you play as the dominant woman, though, this is not something I'd insist on. To be credibly dominant, she should be strong, but more in the fantasy warrior way, not in the real world bodybuilder way. Her outfits should mostly emphasize her dominance, lingerie is for the other milfs and girls. I'd set her apparent age in the early or middle twenties though she might actually be much older (if she is some sort of goddess or Chosen one) or younger, but with older memories (if she is a cyborg or golem).
If you want to bring straight sex into the game, forget the paragraph above. No straight sex for female protagonists please! Then make the protagonist a man - meaning a grown man deserving that name. NO teenage virgins and NO creepy grandpas! If the game is set in fantasy or sci-fi world, powerful antiheroes might work well. If the the game is a mom-son game, make the protagonist what I would call an "alpha villain", a man who can have any woman and therefore seeks the ultimate taboo. Warlords and ruthless business men work well, but my favorite would be a mad plastic surgeon eager to turn his mother into the perfect fuck doll.
