Uchuu Kaizoku Sara

Uchuu Kaizoku Sara (Space Pirate Sara) is a hentai visual novel with a 4-episode anime adaptation featuring a sci fi / medieval like setting. It's protagonist, a space pirate named Sara Scorpion, is trying to steal a magical Laser Blade, and since this is a hentai, she gets caught, sex of various varieties happens, and the story ends on a surprisingly positive note. Mostly.

Based off an H-game of the same name.

Tropes used in Uchuu Kaizoku Sara include:

Alliterative Name: Sara Scorpion
Aristocrats Are Evil: Every single one depicted is shown to be an utter hedonist.
Bad Boss: Sara Scorpion. The Duke, the Twins. Really everybody with a boss-like position is kind of a prick in one way or another.
Bittersweet Ending: Mostly sweet, with Sara obtaining what she was after not to mentioning becoming a queen and by implication punishing her former tormenters and gaining a right hand woman in the process. Unfortunately, the bitter part is that her and Sylia are stuck as futanari, with no way to reverse the transformation. Even that stays mostly sweet, as the two girls that made them into futas agree to become their cocksleeves, quite willingly, in fact!
Blondes Are Evil
Fate Worse Than Death Some of the endings in the visual novel are this. In one, Sara ends up brainwashed into becoming a semi-immortal empress of the galaxy who would actually be the twins' puppet so that THEY would rule forever. In another ending, she and Sylia are made addicted their Futanari states to the point where they take orders from the Twins with that being their reward even knowing they're being used, but then the Twins further manipulate them into "marrying" the Twins and them wanting Sara to impregnate them with her children who would be of Royal blood.
Futanari: Portrayed differently in the game and anime. In the game, Sylia and Sara are turned into this as well as the two young girls who torture them for the majority of the plot. In the anime, only Sylia and Sara are turned into this.
Hero Antagonist: Sylia to Sara, initially. The events of the story invalidate this rather quickly. In the omake set afterwards Sylia is her right hand woman and lover.
Happiness in Slavery: As the short omake reveals, the Twins were so addicted to the now-futanari Sara and Sylia they simply couldn't refuse an offer to be their sex slaves. In the end, everybody gets their sexual pleasure, and Sara and Sylia find justice to be mostly satisfied.
Naughty Tentacles
Nice Job Breaking It, Hero Sara selling Sylia and then getting her crew almost wiped out for her ambitions comes back to bite her. Fortunately, she manages to overcome these issues and atone as well as win in the end against much worse evils.
Nice Job Fixing It, Villain The Twins that captured Sara and Sylia had been trying to brainwash them into serving them as puppet rulers of the galaxy since only Sara could use the Scorpion Blade, meaning they had to take possession of the Scorpion Blade itself. Hans breaks in and steals it, and then gives it to Sara who at first wasn't aware of how to draw on its full power until they pushed her to the point where she DOES fully awaken it and promptly defeats them both.
Omake: A short one set after the main four episodes reveals the girls who tormented them, who apparently died in the main story, are very much alive and are now being used as Sex Slaves by Sylia and Sara as retribution for what was done to them. Their slaves prove rather willing to submit to them. The only sour note is that both Sara and Sylia will never be able to go back to being normal women, as their futanari transformation is now permanent, which was never stated but implied in the main story.
Shout Out: Several characters and concepts are this. Space Pirate Sara. Hans, her first mate, is an android bodyguard to a space captain in a galaxy full of rapist aliens and corrupt politicians... Where have I heard that before?
The Dragon: Sara's first mate, who proves to be the only competent male in the story. Sylia later becomes this to Sara.
Villain Protagonist - Sara is this. Although not as evil as most examples, she's a space pirate who technically participated in some human trafficking to try and get what she was after. She makes up for it by the end though.
What the Hell Hero Sara is a space pirate, she fights her way to capture Sylia who once she catches her, trades her for (information on) an artifact she was after. She makes up for it by the end when she regains the Scorpion Sword and becomes the Empress of the Galaxy by making Sylia her 2nd in command with Hans.