Other prompt fill I did a while back on norsekink
"Loki is Coulson's mother (or father, if you must) and snarky BAMFness runs in the family. FAMILY REUNION TIEM Y/Y?
If he does have magic, Loki sealed it away so he could grow up undetected by Asgard. Don't really care about who Coulson's other parent is, they're not together anymore.
Whether Coulson knows if Loki is his mother parent or not is filler's choice."
Coulson never really went out on fieldwork. But Tony secretly suspected that the agent was a total badass. Not that he'd ever admit that.
But on this occasion Coulson was tossed into the mess like everyone else. Psycho of the week had decided to teleport all the occupants of the Avengers into the middle of his super-secret-lair. Tony didn't bother to hide a scoff, the GPS on his phone had already adjusted the location for his most recent tweet.
The battle is raging between the Avengers who are, admittedly, at a disadvantage considering no one was prepared and the crazy's goons. Stark hears the snap, the yell of pain and the Capt. shouting "Coulson!" before he turns around. The agent in question hits the ground hard, he's been thrown back by one of the bigger robot thingies wandering the lair. Tony can see bone sticking through the skin just below Coulson's elbow. Both him and Thor move towards the injured man.
Then there's a flash of emerald green and Tony sighs inwardly. The last thing they need is the Trickster showing up. The light is brighter than normal and Stark is blinded for a moment. When he regains his sight he's almost scared.
No scratch that, he's fucking terrified.
Tony's seen Loki annoyed, he's seen Loki frustrated, he's seen what he thought was anger on the Liesmith's face. But he never, never seen anything like the pure, unadulterated rage on the god's face in that moment. Tony's just glad it's not directed at him. Loki is glaring daggers at the psycho behind this all. He glances around for a moment, seemingly just noticing the fight surrounding him. Loki clicks his fingers at all the goons vanish. All of them.
Tony swallows nervously at the blatant display of power and glances at Thor, but the god only has eyes for his brother and Tony doesn't like the look of trepidation on his face.
The crazy's laughing maniacally in the corner until he notices the deathly silence that has fallen on the room, only broken by Coulson's ragged breathing. Loki stalks forward, eyes on the man. The psycho pulls a gun from somewhere but before any of the Avengers can act, Loki's turned it to dust. He isn't playing around anymore. Something has kicked Loki into Berserk Mode and Tony can't figure out what. Judging by the confused and worried looks from the room neither can anyone else.
Loki by this point has crossed the room and has the man cornered. He picks the human up by his throat, ignoring the distressed noises he makes. The crazy manages to gasp out a sentence.
"What did I do to you?"
Loki's whole body tenses and he brings the mortal's face close to his.
"You dared to harm my son,"
Tony can barely make out the words the Trickster hisses. Loki drops the man to the floor and waves his hand over the mortal.
Tony has a strong stomach but even he has to look away from the red splatter left behind after Loki seemed to…explode him.
Thor is the first to speak. "Brother…" he starts slowly, not wanting to say anything that would further upset his brother. But Loki ignores him. He teleports to Coulson's side and even as Steve steps forward to defend their injured comrade Loki is helping the agent up. The rage that Tony had seen is gone and in its place there is a tenderness that Tony wasn't expecting in a thousand years.
The Avengers move in closer to Coulson and Loki seems okay with it. The trickster frowns as he inspects the agent's broken arm but heals it in an instant.
Granted, the whole situation was weird but what happened next took it to a whole new level.
Loki was fussing, actually fussing over Coulson. Stark couldn't think of a better word. The god seemed to be checking if the agent was completely fine and Coulson was just standing there with an odd bored look of resignation on his face. Eventually the agent spoke up.
"Well, you should've called earlier,"
"We had it under control,"
"Control?" Loki straightens up, hands on his hips. "I don't think so, your arm was broken, that is hardly under control," he snaps before resuming his fussing, going as far as to neaten Coulson's hair.
"Loki," the agent protests. "Loki, Lo-, Loki, L-, Dad!"
Loki freezes. Along with everyone else. Coulson ignores them.
"I'm fine, thank you for coming when I called," he says sincerely.
Loki's lips twitch up in the hint of a smile. "Always," he places a kiss on Coulson's, his son's Tony corrects himself, forehead and then disappears, just like always.
Natasha is the first to react. "What the hell was that?"
Coulson just shrugs. "Paternity, or maternity I suppose, concerns never came up before,"
Steve looks appalled and is about to speak before Thor steps forward and pulls Coulson into a bone crushing hug.
"Welcome to the family Nephew! I will have to make up all the birthday presents I missed!"