Breaking the Magical Girl (Dark)

This is the story of a girl, a magical girl.  A champion of justice and love.

"Why I should care about love or justice?"

That's what she was at the start of the story at least.

"I could instead be worshiping you."

Her team was fighting an invasion of demons.  Beings who freely admitted they came from "what humans call Hell."  Though they pointed out humans did not have a completely accurate understanding of what it was, or who its inhabitants were.

"Make me betray everything & everyone I’ve ever loved."

They had just slain one of the lieutenants of the demon lord for the first time.  A major victory.  They were about to celebrate when, Zorn, the demon lord, decided to stop playing around.  He appeared and with a single attack, stuck the team down.  Too hurt to move, most of them unconscious.  He easily could have killed them all then and there, but he had a better idea.

"Your monstrous power is too much for a magical girl to resist."

He claimed one of the girls, his soldiers lifting her and following him back to his castle.  He had one goal.  Break her, make her submit, sexually, and as a warrior who would not hesitate to fight to the death for him.

This is likely to be brutal early on.  He will force himself on her repeatedly.  Beat her.  Starve her.  Make her beg for mercy.  Show her images (possibly manipulated) of her team abandoning any idea of saving her, her friends and family forgetting about her.  The demon lord is something closer to a god.  He can appear human, but also monstrous.  A human could not comprehend his true form.  He wears her down, but also rewards her when she starts to become loyal.  Giving her power, luxury, favor as she becomes more loyal and follows the commands he gives to test her loyalty.  Eventually being named as he concubine and bearing his inhuman children, fighting her former friends (and lover?).

That's the concept, I could play either the magical girl, or the demon lord (or both with different people).  This is the end result: