Oh, you little- Why the hell won't you die?! Naoya is a powerful, dangerous man who could kill most sorcerers with a snap of his fingers. Yet you, you little pest, you stain on his reputation, you refuse to die no matter what he does. Do you know how many times he's executed a plan to kill you only for it to fail?! This isn't very pleasant for him at all.
He's got his hands around your throat, it's what he does when he's frustrated...with you. Yet you're not even choking, or even struggling for that matter. What the hell are you? You've been haunting him for years now. You showed up on his doorstep, bound to him, amused by his immediate attempt to kill you.
As you told him all those entertaining years ago, he can not kill a bound celestial. Yeah, you're pretty much a god; you just wanted to play with a human for a while. The embarrassment and frustration he feels whenever he fails to kill you makes you laugh. The rumor going around that you're his lover or wife makes you laugh even harder.
This man is insane with no sense of self-control, and before he knew it, he respected you, and because that doesn't happen often, his respect turned to attraction. After a few times of getting you into his bed, he's pretty sure he has fallen in love with you.
You noticed when the attempts on your endless life stopped and when the roughness started...What? It's not like he knows how to be gentle; he's never been in love before. You know he cares, though. He started making sure you ate all three meals, and he liked having you around him even if you weren't doing anything. He's never been in love, but he's trying because...well...you're you.