A/N: Loki looked so frightened when Thor threatened to strike him in Thor:The Dark World. Here's a little ficlet that is my explanation for that.
WARNING: If you are sensitive to a parent hitting a child for no reason, then please don't read.
Loki had always known that Thor was the favourite. But he hadn't known that his father was so happy with Thor that he was unhappy with him. He curled further in on himself, clutching his throbbing, bruising cheek. Odin had hit him. HIT him. Not an accidental smack or a light whack for interrupting him, no. Odin had turned around with fury blazing in his eyes and stuck Loki hard across the cheek. His gauntlet had caught the tender skin above Loki's left eye, tearing a little, and there was a bruise from where the metal had hit his skin. Loki had fled, tears welling, not listening to his father's pleas and apologies.
He heard footsteps, and slid further into the small gap between the ornate bench and the wall, trying to hide from whoever was coming. "Loki?" It was Thor. Thor. His brother. Safety. Loki wanted to reply, but he was still trembling and frightened and his mouth did not want to speak. He did the only thing he could - he whimpered. "Loki?" Thor's voice turned gentle, and he laid his eyes on his brother. "Oh, no Loki." Crouching, Thor slowly reached out a hand towards him not wanting to startle his younger brother. Loki let him reach, sure that Thor, unlike Odin, would not hurt him. "Come." The elder said, and cradled Loki's hand in his.
The younger teen crawled out from his hiding spot, and tightened his grip on his brothers hand. Thor lead him to his chambers, and sat him on the fine, fur covered bed. He left to get a bowl of water and a cloth, but was back quickly, loathe to leave his brother alone for too long. Carefully, with a care Loki never knew his brother possessed, he ran the damp cloth along the cut above Loki's eye. The dried blood came away easily but the cut still stung. "What happened Loki?" The question was unexpected, and Loki's eyes widened. Surely, Thor would agree with father! HE may strike him!
"Don't be scared brother, I will not hurt you." Well, now Loki felt stupid for ever doubting his brother.
"Father, he..." Loki swallowed as Thor put the cloth down and looked intensely at him. "I, I... had to get an urgent message to him, but he was in the council, and when I, I... interrupted, he turned and he-" Loki cut himself off, feeling unable to tell his brother who completely worshipped their father, how Odin had turned and struck him with such malice and cruelty. However, it appeared that his silence spoke, and Thor's face immediately filled with rage. Loki trembled and scooted back on the bed - he knew his brother would hate him -
Gentle hands grabbed his head, and all of a sudden his face was buried in Thor's neck. "He shouldn't have done that." Thor's voice was soft, but the edge of anger was still there. "I am sorry little brother, and I promise to never lift my hand to strike you." A grateful tear welled in Loki's eyes, and clung to his big brother, feeling so, so safe. "No matter how much you annoy me." Loki chuckled and shuffled closer.
He'd thought for certain that Thor was about to hit him the same way father had all those years ago. He had the same rage in his eyes as Odin had had when he'd struck him. Since finding out that he was adopted, Loki had never felt so scared, so full of fear. He looked at the hunched back of his big brother, crouched over his mortal lover, and felt the same way he had all those years ago - scared, fearful, vulnerable. Loki looked at his hands and found them trembling, almost imperceptibly. He felt the phantom bruise, and remembered the sting of the cut. "I'm sorry little brother." Thor's voice was soft like it had been when it happened, and Loki looked back to him. "I'm sorry." Loki smiled a small smile.
"At least you kept your promise." Thor smiled back.