Disclaimer: I'm wanting to try this game out in order to see if my muse is still up to the task of posting. Please be warned that I can't make any guarantees about how fast I'll post to this game or how long it will survive. If that's okay with you, please keep reading. :)
The canon of the Metroid series is the basis for this game, but it's not so much about the setting as it is about the relationship between Samus and your character. Don't worry about canon at all! If there's something canon we need to address, I can either explain it to you or we can gloss over it.
Though Samus Aran was born human, after her home was razed by the Space Pirate known as Ridley, Samus was taken in by the mysterious bird-men known as the Chozo. They infused her with their genetics and trained her to be a warrior. Samus became a 6'2" (1.9m) powerhouse of a woman, and could have done many things with her prowess. She chose to become a bounty hunter. Still, she was not an amoral character. Most of her contracts come from the government of her own species, the human arm of the Galactic Federation. She has taken her tormentors, the Space Pirates, to task dozens of times over the years, threatening to singlehandedly drive them to extinction while protecting other planets they threaten. Samus is one of the most formidable forces in the galaxy at large, however, Samus' life has been a lonely one. She was not given much time to learn about her species in what little time she had before her colony was destroyed, and she could never see eye to eye with the Chozo, her mentors. When she returned to Federation space, she was able to communicate with civilization, but struggled to understand it. Destruction and combat had been her language since childhood, and so she kept her distance from anyone not involved in her missions.
This is where your character comes in. Samus' previous handler, Adam Malkovich, was killed in action. Samus was out of contact with the Federation for a year afterward, taking on jobs on her own. A new threat has arisen, and the Federation needs Samus once more. Your character will be Samus' new handler, tracking her down and wooing her back into Federation service, and wanting more after they get to know each other. The main focus of the RP will be their relationship, and your character should be a combat veteran as well, so that Samus can respect her and also leave us the option of having them go on missions together.
Like I said in the title, I leave it up to your preference if Samus is a futanari or not. I'm happy either way. I would, however, like your character to be female.
I'm only going to be running one instance of this game, so please PM me if you're interested, and please understand that it's nothing personal if I choose someone else. :)