Intro. Aida is your 14 year old step sister your adventuring parents adopted from a dead guild member.
She is gifted in magic and tried to proof to be a worthy mage until the day she tried practicing some forbidden magic when she was 9, setting off an unquenchable fire that killed your parents. This fire scared your sister's back and your chest when you pulled her to safety and she has been feeling guilty ever since.
She pulls an air of indifference and haughtiness when in front of you but you have seen her crying body wracking sobs even alone. It seems she's trying to be prickly to make you give up on her she leave her so that you will be free from the burden of taking care of her.
You will never let her go, because she's your sister and you've promised your parents you'll protect and take care of her.