[@Xaltwind] Thank you for your answers! May i ask another, if that is ok? :D

Could a child be born from two mixed bloodlines? Or in other words, this idea kinda: 

"Say her great-great grandfather on her father's side was a half-demon. Then her great-great grandmother on her mother's side was half-angel due to some divine boon to ancient ancestors. The bloodlines were notably watered down, until her respective sets of grandparents jumped ship from their families and hid their true bloodlines from their own children due to issues, old family extremism, or others reason that they wanted to leave and hide away for. 

Eventually the child's parents meet, and not knowing their ancestry marry and have a child. This child would be the OC. 

The opposing ancestry inherited from her parents causes those genes/latent traits to awaken each other, and her mother's pregnancy is filled with illness, weakness, suffering, and eventually barely surviving giving birth to the OC herself. 

The OC, on the other hand, always cries as a child due to her body trying to adapt and survive with these greatly awakening magical aspects in her blood. Even once she becomes adjusted in regards to her body, she suffers a constant pain all the time due to her genetics. In return, however, she get a rather high magical potential and perhaps a rare or unique magical class to fit her natural abilities.  

Of course this child is not trained, but will be more sober for her age despite possessing some naturally childlike traits. 

Her parents were then eventually killed in a plague, leaving her to survive and wander the streets as a sort-of urchin. Her passive abilities, though untrained and whatever they are, allowed her to 'hear' the voices of her respective demonic and angelic ancestors...guiding her, giving her info, teaching her to survive and such.

Then when the Isekai Guy appears, they guide her to 'seek the man from another world', and though she knows not why she leaves (even after becoming a famous and respected local 'street oracle' or something back home in the following years after her parents' deaths. Though she is just a kid, not a super trained mage...but with actual training she'd definitely maximize her potential." 

Asking about this, to help cement for sure if I'm joining or not. Cause i would need a compatible idea, tbh, haha! 
(TwT)