oh man I'm asking for trouble. LOKI, TIME LOOP/TIME TRAVEL
An adolescent Loki, still a century or so short of his majority, discovers a time travel spell in a forbidden grimoire, and desperately wishes to try it. Of course, time magic is illegal, so he has to be cautious; he ultimately chooses to go down to Midgard to test the spell, since it’s a backwater realm and not densely populated. It’s a fair place for a test run, and one where he’s unlikely to cause a paradox by running into his future self – after all, what possible reason would he have for wanting to go to Midgard?
Of course, the premise of the spell is imperfect. It’s theoretical, and has never worked. But in his studies, Loki thinks he finds the problem – the key to making it functional. So he modifies the enchantment.
But the spell exists in a kind of quantum uncertainty, where casting it creates a bifurcated timeline; in one branch he succeeds, and leaves the timeline; in the other he does not, and remains in his present.
Loki however, wants to discover what destiny lies in store for him, and the exploits of his future self. Traveling to a future in a world he hasn’t occupied is useless to him – so he modifies the spell even further, to forcibly merge the timelines.
Unfortunately, this creates a massive quantum instability of a universe where there are two Lokis, and where the spell simultaneously failed and succeeded (The one Loki who time-traveled, and the other Loki who only remembers the spell not working and getting yelled at for a long time for trying when the Allfather found out).
And of course, the younger Loki – the one who traveled – is now on Midgard in the modern day, and is attacked and taken into custody by the Avengers for reasons he doesn’t understand.
It’s a strange and terrifying future, and he is beginning to have regrets. But he manages to convince the Midgardians that he isn’t who they think he is once Thor of all people turns up. Why his brother’s future self is spending time on Midgard, Loki also can’t fathom, but he’s relieved to see him all the same.
Thor’s heart is swelling and breaking all at once as the truth emerges, because this is the brother he remembers. This is his Loki; before it all went wrong. And now his friends can see how his brother once was, when he was witty and clever and hadn’t been lost to madness and cruelty.
But the Loki who has been lost – the mad and cruel Loki – is still at large. There are two Lokis now: past and present, and their simultaneous existence is weakening the fabric of reality. All too quickly, younger!Loki realizes that he can’t go back, either – if he goes back to the origin point of the spell, that conscious version of him will cease to exist as the timelines collapse, and only the version who grew into the Loki-who-fell will remain.
And Loki doesn’t want to stop existing; doesn’t want to die.
But the universe is tearing itself apart. There can only be one Loki. And so he comes up with a plan.
Loki is going to kill his other self.