His lips form a tight line at that, and a scowl crosses his face. Thanatos doesn't ask much of mortals. He doesn't want rituals or sacrifices, he doesn't crave worship, but to simply not believe they exist at all? After all of the work he does to keep things running smoothly? And just after this rather harrowing ordeal for him, too.

"To be thought of as an old superstition..." In trying not to show any emotion, he inadvertently shows WAY too many, his arms crossing protectively over his chest as if it might guard his heart from being seen, his eyes cast to the floor as he tilts his head away, hoping his expression is unreadable.

"... Why should I care what mortals think? Even if they're terribly disrespectful. The other gods will set them right if they care to, anyway." And since Hypnos is the way he is, he probably wouldn't care if someone used his name as their own, he guesses. It doesn't stop Thanatos from secretly wanting to stop her anyway.