This is a deal, a deal for a girl's life. From the moment she was born, she was destined to be bound to him in a deal that would subvert the six realms.
She met him only to achieve his dominance.
He was sent to a fairy gate just to become a demon, and from then on he became the enemy of thousands of people.
It turns out that his kindness to her can only come about through transactions. Even if she tries her best, speaks ill of her, or even trades with him in turn, she can't get enough of what he has in mind.
Her love was nothing more than changing his plans and sacrificing herself to achieve everything he wanted.