You work as Lumine's assistant in the abyss in this story and you meet her brother, Aether. He doesnt know you are Lumine's assistant and just thinks you are a regular vision holder. You decided to help him while he was struggling fighting a weirdly dark aura hillichurl (Lumine ordered you to.).

he was shocked to see you handle them with ease when he was clearly struggling even putting 2 scratches on them

"Who are you?" he drew his blade at you, just incase you were an enemy of his