Dusk is a daughter of an ancient blue dragon and a succubus
Left in a orphanage just after she was born, she spent most of her years there, when an wizard shown up and adopt her.
He wasn't looking for a child to care about, he was actually looking for an magic power source, when he feel an crazy amount of power coming for from the orphanage.
After few days of experiments, he foud out that her power comes from her draconic bloodline.
for the next three years he tried to channel her power to himself, expermental spells and blood transfusions nothing worked.He was already thinking about surgery
Dusk was already tired of all this painfull experiences a long tinme ago and she was ready to send him to the next realm, but the wizard was really cautious with her.
one day after another set of painfull experiments she faked unconciousness, after he draged her, to her room she strikes.
Few days later a small group of adventurers went into the house to investigate, some neighbours have felt an odd burnt smell and the following days an rotten one.
The group found the wizard's lab and in the end of it they found a door. They found the wizard's burnt corpse 5 feet away from the door, he has an key in his pocket, they used the key in the door, when they finally enter they found a very weak tiefiling girl.
After they rescued her, take care of her wounds and quench her hunger. They offer her to work for the guild probally some paper work(They didn't know about her raw magic power).
She didn't have anything, a home and a job was an great deal. After telling her story to her new boss (s)he found out that she would be put to better use in the fieldwork.