Sounds like a bait. They're making it out like he's the reason for her being summoned, but I doubt that's the case. He likely just believes she, as a "child of gaia", belongs to him. Probably because he is obviously narcissistic. They also don't look like demons, especially that messenger character. Granted, most stories (such as Rain), do not depict demons as anything more than humans with extra parts- and they didn't show this badboi's forehead. But I, again, believe this to be a red herring.
Also, if he really were the person in question, isn't it a little too early? There's only been one form of real drama, not counting the church's appearance. This story would be rushing towards one of the major plot points a little too fast. These types of things need to stay shadows looming over the characters for as long as they can be. #Opinions