You want some spoiler?
Alright
SPOILER ALERT
From what I understood,the blond girl's mother (the first wife) was neglected by the fl's father and was abused by the fl's mother.
When the first wife gave birth to the blond girl,the baby died, so she sold her soul to the demon just to save her baby, she died including the baby.As for the demon being itself, instead of saving the baby he possessed it instead.
So inside that blonde girl isn't her real soul but the demon,and the demon's real intention is to kill the FL so that the god will abandoned the place (he ruined it)
Actually to be honest the real bastard here isn't the demon but the father.
He knew everything, first wife's life in the second wife's hand, he also knew that the FL is his real daughter, yet he killed her for his own sake without knowing the result, and at the end the FL forgiven him like nothing happened!!!
I don't know if this was the real translation but at the end they would go like...
"I'm Home"
the dad was like "Oh I thought you're not coming back"
And she replied "nah,this is MY home after all"
"Welcome back"
She was supposed to cut all the ties, take her brother with her and live happily without her father!!! Damn it
THAT'S A DEMON SHE'S ALREADY DEAD !!!LEAVE HER ALONE YOU IMPOSTER!!! ヽ(`Д´)ノ (╬ ̄皿 ̄)凸