Arwen's story begins a few hundred years ago, in the Old World. A prosperous city-state that was accidentally built near a portal to the First World. A flock of Unknowns came through, and some settled in the surrounding forest.
A few hundred years later. The city-state ruled a mighty empire spanning thousands of miles. And a sprite girl was born to the Arwen family in the forest. Her mother named her Andebrocirix, a name that she would hate all her life, instead opting to be known by her family name.
When the Arwen was fifteen, the ruler of the city decided to demolish the forest to build himself a new palace. Arwen's family all died in the fight, and it fell to her to be the leader of the resistance. She lead the sprites to victory after victory, and everyone expected the human king to give in and grant the woodland to the sprites.
What happened instead was something no-one, neither Arwen nor anyone else, could have foreseen. On Arwen's 16th birthday, the forest was razed to the ground, and Arwen, along with over a hundred other sprites, were now refugees. The sprites formed a new community a hundred miles away, but the king sort out Arwen, and attempted to have her murdered.
Knowing she was not safe, and nor was anyone who was with her, she fled. She walked thousands of miles alone, eventually coming to the sea. She stowed away on a ship bound for a distant shore, and on being discovered whilst cargo was being unloaded to go through the The Portal, she was told that she could go unpunished for stowing away if she signed up for the Explorers' Guild and headed through said Portal. For her, this was a dream come true. She knows that the king could not track her to the New World.
And thus it came to be that Arwen who is named Andebrocirix entered into a better life. A better life... Beyond the Portal.