Moon
Truth be told, Hades had no idea what was so special about the moon. It hung in the sky and provided some light, but it was no sun—and for that he was thankful as he adjusted his sunglasses to the upper world's light.
It didn't give the mortals the light they craved, nor did it twinkle like the stars, and some nights it was absent entirely from the night sky. No, Hades failed to understand what was so special about the moon that his wife made it the centerpiece of her speakeasy, complete with binoculars trained on a stubborn crack in the ceiling that had been there from the moment he claimed the Underworld as his.
He shook his head. Whatever their reasons, it was undoubtedly dangerous, and he considered how best to curtail it. As long as the moon was contained, Hades knew, only seen in glimpses, there'd be no trouble.