Curate, connect, and discover
So Merlin is Immortal, he can't stay dead, but he does get killed throughout the show in his bid to protect Arthur.
Here's my AU idea:
Every time Merlin dies, a piece of his memories dies with him.
This doesn't affect him much, as he doesn't die often in the beginning, but as time goes on and he gets more desperate to protect Arthur, he becomes more reckless, not realising his lucky escapes after being knocked out was due to him being dead and the perpetrators leaving his corpse.
After all, dead men tell no tales, usually.
With each death, he loses a memory and he wouldn't have noticed, but Arthur does.
Arthur would mention at one point or another about this or that and Merlin wouldn't be able to recall it.
It at first annoys him and makes him point out about Merlin's low intelligence. But as time goes on, he gets concerned when Merlin can't remember certain people or events.
He brings up the time Merlin cried for the Dragonlord.
Merlin: Who?
Arthur: The last Dragonlord? Balinor? You cried over him when he died protecting you?
Merlin: Huh... I don't remember him, but if he did save my life, then I'm grateful, but why did I cry? Did I know him well?
Arthur: ... No, but you helped to convince him to help Camelot. He was a good man in the end.
Merlin: I see. Well, it's strange how I don't remember that.
Arthur: *Concerned*
It happens occasionally as time goes on and Arthur starts to consult Gaius about Merlin's memories.
Then I can see Merlin being outed as a sorcerer to Uther when Arthur is gone on some diplomatic mission. Uther wouldn't think twice before sentencing Merlin to death. Only he won't die.
He dies and dies in many different ways. Uther desperate to get rid of Merlin who he sees as the embodiment of his fears (if only he knew 😅).
Merlins deaths happen so many times, that by the time Arthur returns 2 weeks later, and storms the dungeons angry and confused, he was met with a sight he'll never forget.
Arthur: Merlin! *Rushes to the jail bars and demands answers to his questions*
Merlin: *Stares blankly*
Arthur: 😠Merlin! Answer me!
Merlin: Do I know you?
It hits him harder than any fist or magic ever could.
And that's all I've got. Tell me what you think, what happens next?
Till next time fellow dreamers~! ✨