This is how Gabriel first became Loki. And Gabriel isn't meant to act like he does on Supernatural just yet. It is only natural for him to be angel-y before he becomes Loki.
Disclaimer: I do not own Supernatural. It belongs to Eric Kripke and the CW.
An angel, in his true form, was sitting on a boulder overlooking the sea in somebody's heaven. He knew that it would take a while for his brothers to find him. He always found refuge in someone's heaven, knowing that there were billions of them, and no angel would be able to look for him in all of them before he escaped to a different one. He closed his eyes and tried to find comfort but it was hard for him to. His brothers were slaying each other without mercy, without second thought. Just earlier that day, Hael had been killed by Lucifer for denying to join him, and Michael killed Muriel for joining Lucifer. It hurt to see his family hurt each other and lately, he'd felt like leaving it all behind. Maybe if he didn't see them again, he would be able to pretend it wasn't happening.
Maybe if he could find a vessel... He let his mind reach out to the world, to all the possible vessels he could use and was surprised by one. One of his vessels was a... pagan. Loki, the Norse trickster god, was a vessel.
Loki was the son of Farbauti and Laufey and husband of Sigyn. He knew how that story would end... Loki would be tied down by the other Norse gods under a serpent whose venom would drip on him as revenge for killing Baldr. Then, Loki and Heimdallr would kill each other during their version of the apocalypse.
Maybe if he promised Loki to avoid that fate, he'd let him use him as a vessel. No angel would think a pagan could be a vessel, much less would anyone think that an angel would accept a pagan as a vessel.
Yes, that's it, he thought as he stood up. I need to speak to Loki.
He descended upon Earth and let his mind pull him toward the pagan's location. He was swimming by waterfalls, disguised as a salmon when he found him. That must mean that he was close to being found and tied, like he was fated to.
"Loki, show yourself. I am an angel of the Lord." Only a vessel could see an angel in its true form so he didn't have to disguise himself to Loki.
"Who is that? An angel of the new god?" Loki's voice was like honey, but at the same time, that voice was filled with an unspoken taunt.
"It is."
"But your Lord is not mine," Loki replied. "Whatever it is, I refuse to comply. For your Lord, I will not put my life on the line. Don't you know that the gods are after my head? You must leave at once or I will be caught. Time- that's something I haven't got."
"But I do know your fate, Loki," he said. "You will be caught and be bound by the insides of your own son. You are my vessel, let me in my true form take refuge in you. If you allow me to, I can heal you. You will never die."
"Ah, you think this I didn't know? I do, and since a long time ago. But I refuse to go down, not without a fight. Odin wants to do this out of nothing but spite."
"Did you know that you're to die at Ragnarok?"
This Loki must have not known, because after a few minutes he reluctantly said, "Fine, I accept. Only because I have no choice. You can use my power as well. Except," he paused to shift back to his true form and come out of the water, "you may not go near my family."
The angel thought this over. "I accept your terms."
Without a warning, a bright white light stopped the Norse gods that were approaching, looking for Loki. Some of them, knowing that a heavenly being was present, shut their eyes. The others, crumpled to the floor, their eyes burning out.
The angel, now in Loki's body looked up. "Goodbye, father," he said as he disappeared. He was no longer Gabriel, the archangel. He was Loki, the now rogue Norse god.