Engetsu
"Kyah!" He yelped at the flicker, his fangs showing in his gaping distressed expression, only for the poor demon to droop subtly at her reprimand. He wouldn't do it again, absolutely not. Still, being this close to her, and being figured out so easily. It was all so embarrassing.
His eyes traced downwards, trying to hide a small blush. Then, he turned to face her and talked to her truthfully. "Do you remember when I told you I was a demon? That was mostly correct. But I didn't exactly paint a full picture."
He took a pause, thinking of where to exactly begin. He didn't want to ramble tirelessly and annoy her. That was the one thing he did not wish for. He didn't know why, but seeing her displeased face once more was something he simply couldn't bear at the moment.
"Usually, a demon will be formed from a strong desire. It doesn't have to be negative, any strong emotion can do. Because we are made of emotions and desires, powerful feelings can change us, either in positive or negative ways But emotions that outright change the way a demon interacts with the world are rare, and usually very powerful."
He shifted his gaze back, then focused back. He clasped her hand and brought it to his chest, so he could feel her pulse. He had tried to hide this shameful side, but it was no easy feat. He wanted to be closer to her, to protect her and to be hers and make her his. Even now, these insidious feelings were lingering in him.
"A human might be able to find ways to cope with a mental manipulation. It isn't always the case, but sometimes its much harder for a demon to do the same, especially when that emotion was already there to begin with."