It starts with a spell that should have turned you into a mouse.

Merlin’s eyes glow gold, the air hums, and… nothing. You stand there in the middle of Gaius’s chambers, arms crossed, staring at him like he’s the idiot in the room.

“I swear it worked yesterday,” Merlin mutters, pacing, hands in his hair. “Arthur turned into one for a full hour.” “That explains the squeaking,” you say dryly.

He glares at you, then softens, because he always softens with you, even when he pretends not to. “Right. Again.” “Merlin-” But he’s already casting another spell, this one meant to heal the gash on your arm. Warm light spills over you… and fades instantly, as if it has no place to land.

The cut remains.

“Are you doing something?” he demands, walking up so close you feel the heat of him. “Yes, Merlin,” you deadpan. “I am resisting your magic out of sheer spite.” He opens his mouth, then closes it. “…Fair.”

But after that? It gets worse.

Love charms don’t stick on you, Illusions flicker out the moment you blink. Even the enchanted roses he tries to conjure for a laugh crumble the second you touch them. You become a puzzle he cannot put down. At first, it’s just curiosity. Questions. Experiments. Subtle spells meant to test the boundaries of your immunity. But soon, Merlin is watching you with something else in his eyes, something hesitant, something warm. Something like a question he’s too afraid to ask.

One evening, long after Arthur has gone to bed and Gaius is snoring upstairs, you sit with Merlin in the dim light of the hearth. He’s pretending to read. You’re pretending not to notice the way his gaze keeps drifting toward you. Finally you sigh. “You’re staring.” He startles. “I’m observing. There’s a difference.” “Oh? And what exactly are you observing?” “That nothing works on you,” he says quietly. “Not even the spells I can’t control.”

He sets the book aside, fingers tapping nervously against his knee. “It’s like magic can’t… touch you.” His voice softens. “Except I can.”