First off I will show you my references, I want to go for a baroque inspired Setting. I would say I aim for a dark Alice vibe. I really like a mixture out of creepy and cute, so I am excited if I can combine both.
I drew a concept based on this for the past couple of days and came up with this:
To really get her personality right I expanded her background story.
Greta was born into a wealthy household. Her mum died when giving birth to her which led to her dad holding a grudge against Greta. When she would grow older nothing she did was right. Her dad started abandoning her, either he would shout at her for not being good enough or straight up ignoring her. Greta became a very sad and lonely child. Her frustration and despair attracted an old ancient being. A blood demon tried to form a pact with her. She would gain his power and he would join her in her body. When the pact was formed the anger in her head overthrew her whole body and Greta used her new powers to brutally kill her father. Shocked by her actions she tried to fight the demon within her, but it was too late. The demon took control of her mind and body, pushing back everything she was before. Now the demon takes her body to establish his power on earth, if Greta is still somewhere in there remains unknown.