Backstory: Wariscoming AU Loki was born female. Otherwise, the story begins much the same way - Odin adopted the stolen Jotun infant, made her part of the family as though she were his own child. She grew up Thor's younger sister - the princess of Asgard - and treated as though she were a delicate creature made of glass, for a long time. She was allowed to learn magic - magic was women's work, after all - but otherwise was left to spinning and weaving and learning the proper diplomacy and things she would need when she was inevitably married off to whatever realm's prince needed a bride, in the interests of creating a stronger "peace" between them. She would never truly rule, only sit beside some prince or king, far from home.
It was grating for someone with the independent nature Loki had, and when she complained that it was hardly appropriate that she was treated as nothing but an object of value, her concerns went unheeded. She was eventually allowed to learn alongside the others, when Sif and Thor both spoke in her favor, though Thor did it more to humor her than anything, and Sif's words bled of pity.
Rather than bonding over their shared attempts to resist the male-centered ways of their society, Loki was bitterly jealous of Sif's fighting prowess, her natural talent for physical battle. She was far weaker and while she was fast, she was never able to outmatch the other woman. Thor and his friends seemed to find it endlessly amusing - the mockery of it was far worse than the failure itself. When she confronted her brother, he told her she was taking it too seriously, essentially dismissing her concerns - and her as being simply an object to trade away to another realm. What did she need to fight for, anyway?
Thor's coronation - and Loki's imminent betrothal - was drawing near, dignitaries from all the realms brought in to celebrate and feast, when Loki set her plan into motion. There was a celebratory feast, the night before the ceremonies were to take place. Drunk on ale and reckless with the heady thrill of a plan well-placed, Loki allowed one of the ambassadors from Jotunheim a little close, the two tucked away in well-hidden corners and playing at flirtatious and flattered, manipulating him for her own entertainment -
- until his skin met hers and suddenly everything came crashing down around her. All her plans, her entire understanding - pulled from beneath her as a blue tint crept up her skin, and her eyes blazed red. She killed him, small sharp knife and magic flaring around them so no one could see, no one would know what she'd done or what she was, and the body was slipped into the space between spaces for the moment, and she followed, bloodied hands and gown cleaned away, blood-red eyes bleeding back to green. She would find a way to dispose of it. Of the body, of the secret. No one could know that she was less than even a simple object of value to Asgard - no, she was not even simply a treasure, she was a bargaining chip, leverage.
While her combat skills were lacking, Loki's advantages lay in her ability to enter places unseen by even Heimdall's watchful gaze - her silence as she moved through the shadows to Sif's chambers. She left the fallen Jotun there, a touch of magic on Sif muddling her memory of the previous night, a bloodied knife in her hands.
Come morning, her brother's betrothed was found to have murdered one of the dignitaries, and was judged for her crimes before the royal family. Odin's ruling was death; he did not wish it, but she had supposedly killed a very important person on Asgardian soil - if he wanted to avoid another war (without moving his unwilling pawn), he had to deal with this accordingly. Loki remained impassive and cold during the proceedings; Thor, however, reacted with about as much maturity as an angry drunken troll, screaming and throwing things, making threats.
He was banished to Midgard, human. Sif was executed. Loki had, in theory, won. With Thor gone, her marriage arrangement was to be postponed until her brother returned, as she was the only lawful heir if something should happen to Odin. She had her freedom. She had some glimmer of value again.
So why, precisely, did it feel as though she had lost?
TL;DR: Basically, she went from "ugh I hate that people think I'm just a shiny thing to marry off" to "woah I'm not even a shiny thing I'm just a fugly blue thing" and decided enough was enough and it was time to start cutting bitches. Quietly. Secretly. Also, issues.
She's not evil, and probably won't be trying to kill anyone in Lawrence - maybe Thor. MAYBE- she was just sort of... frustrated. She's just gonna be cold and manipulative and generally doing everything ever to hide the fact that she has no idea how to be a person anymore.