Push her energy into him

She decided to **** as much of her energy into him as she could, and only stopped when she felt a little dizzy. She stepped back, breaking the kiss. He looked at her, and as she watched, shock and horror on his face gave way to a smile of adoration. At the same time, he began to transform, losing his horns and wings, and his eyes and skin changing from a demonic red to a more human bronze.

"My Lady Sarah, it is an honor above all else to be chosen as your concubine and servant."

"I... you what?"

"Ordinarily, whoever kisses the other absorbs their energy and becomes their servant. If they kiss each other, they are married. However, if there is a large power imbalance, the weaker one can end up absorbing energy to the point of it suppressing their own. In that case, the weaker one becomes less than a spouse, but more than a servant. A concubine. My demonic energy has been suppressed even to the point of becoming human. I cannot revert to my true form unless you wish it."

"Why do you seem... okay with this?"

"As a demon, I follow the rules absolutely. A demon's love for his wife is absolute, and his obedience to his mistress is absolute. My body and mind are at your command."

This was weird as hell, but she couldn't deny that it seemed true. But what should she do about it?