very dark & very complicated mutants' au
so, here's the deal: there are mutants on earth. there's a group of them who realises that the government's about to wipe our their mutation with a “cure” that makes their abilities unusable. they try to go there and fight the villains in order to protect the mutants and have them keep ther powers and be proud of their abilities, as they are the next step in human evolution.
there are three main characters (but you can add as much as you want in the background too). let's call them a, b and c. a and b are already in an established relationship or they are about to reveal their feelings to each other (a's powers is healing and b is a telepath). c is a shape-shifter, but the team doesn't like them very much (they are an ex-criminal mutant or something like that and they're trying to repent themselves).
during the fight, b is mortally wounded. a is very far away and can't do anything. c says they can't go back to a and the rest of the group after what they've done and feel loads of remorse about b getting shot. b then decides to implant their memories in c's head and tells them to take their place, shape-shift into b and then pretend they lost their ability to be a telepath, and that c is dead in the fight. c accepts and goes back into the group and follows the plan.
now, you can have multiple endings to this thing!:
1)b dies. a doesn't know about it. c gets used to be b and ends up falling in love with a. a never knows about the swap and ends up falling in love with c. b is dead for nothing and you can cry.
2)b is alive. and c ends up noticing something different about their partner, and ends up yelling at a until they go back and try to find a, who's somewhere in the nature.
3)b is alive. but they've lost their memories and they've been brain-washed to work for the enemy. b attacks the mansion where the mutants' group lives and sees a. a realises they were with c who has to explain themselves before trying to save b once and for all.
4)b dies. a ends up noticing the swap and c explains them everything, so a just curses c by telling them they'll have to be b for the rest of their life. a is now cursed to have a replacement for their former love for the rest of their life, a copy of the dear person they used to be so much in love with, b. b is dead for nothing once again, you can cry.