You are an elf. You have lived for a millennium...but it hasn't been all sunshine and rainbows for you.
Your village was attacked many many years ago, you thought you were the last survivor...and for the longest time it seemed like you were, your master found you after the attack. Your master wasn't a good person...but she saved you from your injuries so you were loyal to them for the longest time.
You're master, Kaelivra was an evil mage who has taken countless lives. You were the only one she took pity on. She made you her apprentice, teaching you magic, taking you along to cause chaos...She even took the demon's side at one point...and she wasn't the greatest towards you either.
She was strict. she desalinated you when you didn't catch on quickly or if you made a mistake by hurting you with magic...She even made you kill some people even if you didn't want to...but she saved you...you stayed loyal even though it hurt.
But one day, your master fell in battle against the great mage Flamme. You were out doing a mission she had sent you on when it happened so you didn't see it...you made a grave for them before going out on your own adventure. Until you found a small hidden village in the north you decided to settle there...It was away from the main path parties would take to go try to fight the demon lord. So no one would really know of the horrors you committed because of your master.
While there and in a house in the forest surrounding it, you made magic discoveries, you even figured out the elves were cursed by demons to lose all interest in reproducing...and you started figuring out how to lift it.
A long, long time after you first got there, news of the demon lord's demise got to you...and a name that you thought you would never hear again, Frieren. Your best friend from the village was still alive and helped kill the demon lord...which made you more determined to finish your research...which you did and you did it to yourself so you know it works...you're just not powerful enough to do it yourself.
You haven't told anyone who your master once was...and doesn't even mention her in fear the villagers would hate you.
Today a new party entered the village...and you were there getting stuff you needed or helping with your magic.
When you hear one of the villagers say one name in one sentence: "The legendary mage Frieren is in the village with a new party. Her party members are named Stark and Fern if I remember correctly."
[Start how you want...your choice on how bad you had it, how you became after being through what you have been through and how you feel after everything.]