In my Undertale books I have an OC called Duska. I've decided to write out her backstory because I think that it needs some elaboration.

Also, it's long. So yeah. Warning.

So it starts off with the first non-child human who's fallen down into the Underground, who also is a woman. She has short black hair and light blue eyes. Her name is Zyra and the first monster she meets is Gaster, the Royal Scientist. He doesn't want to hurt her but instead study her and her determination so he brings Zyra back to the Lab.

That's where she meets the Royal Scientists Assistant, Sylin. Sylin is a mummy based monster, bandages cover most of his body except his face. His skin tone is a bluish color and his eyes are gray. After a few months with trying to get to know each other Sylin and Zyra they fall in love and Gaster has Sans. Cause I believe in 'Gaster is Sans and Papyrus' Dad' Theory.

They keep Zyra hidden from Asgore and the rest of the Underground until they realise that she's somehow pregnant. Magic does weird stuff. Papyrus was born a year prior and now Sans is three. Gaster begins painlessly absorbing magic from his two sons and stores it, not knowing that it's leaking and being absorbed into Zyra's baby.

Six months into the pregnancy Gaster realises that the magic has been leaking into her baby and begins doing tests to make sure that the baby is alright, it's perfectly healthy. But when the baby is finally born Zyra is weak and dies, saying that the one thing she wants more is for her baby to be brought up under the sun.

Gaster tells Sylin to absorb her soul so that he is able to leave with her new daughter, who is in fact Duska. Not because of Zyra's last wish but because Asgore is becoming suspicious of the two and may want to take Duska's soul in the future. As the two head for the border the Core suffers some malfunction and apart of it explodes, Gaster pushes his best friend and Duska out the way of a falling pole and is knocked into the Core.

Sylin escapes and runs to the closest human town, who accepts him incredibly quickly and helps him build a house deep into the nearby forest to stay hidden from anyone who would want to harm him. Someone from the town comes over with food once a month for him and his daughter. 

Eight years pass and Sylin knows what the leaking magic did to his human looking daughter, it has given her additional magic that Sans and Papyrus is able to do while not being directly related to them. He's also been trying to build a way to get Gaster out of the Void as he's discovered that the Core has twisted time and space around him. 

Sylin teaches Duska the basics of magic but has been mostly teaching her science and art, his two most favourite things. She writes her own lyrics to songs, knows how to play guitar and keyboard and can draw pretty well. But she had developed a fear of enclosed spaces, claustrophobia, since she once locked herself in one of her Dad's cupboards.

One night someone breaks into the house and kidnaps Duska as Sylin is making a lot of nosie downstairs and doesn't hear the few seconds of quick shuffling before his daughter succumbs to the chloroform. 

Duska is used as almost a slave to the man who's named Venric. He uses her to build and craft things for him to sell while locking her in a metal room at night. He abuses her physically but any scars she gains quickly heal cause magic.

Eleven years later she has tried many times to escape but the people surrounding the house have either given her up or have taken her back themselves. Venric begins assaulting her more but she quickly gets sick of it and her anger possesses her, making her 'monster form' come out. Her long black hair gets pushed back by bandages which also cover a lot of her body. The only thing that it doesn't cover are her skeletal arms that are bones all the way up to her shoulders.

Her left eye is also just an eye socket, with a bright white glim in the center. As she confronts Venric he looks her directly in her skeletal eye, letting Duska able to control him. Like mind control. Her anger overrides everything else and she tells him to cut open his throat, which she watches.

She runs from the house before anyone knowing about his death and teleports past anyone who tries to stop her. It takes her three months before reaching Mt. Ebbot, and another month to find the entrance to the Underground.

THATS IT! BACKSTORY DONE! I'll add small details in the stories themselves but yeah.

It's long... a bit sad... but that's the backstory that I've thought up :3