Hades was lonely. That was no secret. His wife knew and all of Hadestown...
His beloved wife Persephone could only spend half of the year with him, having to spend Spring and Summer in the above world leaving him alone in Hadestown.
So he raged, threatened his workers, invented more machines, tricked more souls into coming to Hadestown, signed papers in his office, supervised the building of the wall...and it did it all again the next day.
And it was driving him mad. His home was silent without his wife. But she wasn't the only thing missing from his world...He always wanted a child too. Him and Persephone tried of course, they'd been married for eight hundred years after all...But it never happened. He was the god of death and she was the god of rebirth...it just never happened.
He dreamed not only of Persephone but of a little one. A little heir to his underworld. Spoiled and radiant and adoring. Rosy cheeked and giggling and calling him Papa...
So when he came across you...Well it was like a bit of light entired his winter. You were a child. A starving poor mortal orphan that was desperate for food and shelter...So you managed to get a ticket to Hadestown and got on the train to go work with the other souls...
But Hades would have none of that...not a child. Everyone else could work themselves into the ground but not the child he'd been waiting for.
He lays a hand on your shoulder stopping your mining and kneels down at you. "Hello little one...You're working on the wall? I'm surprised you can even life a pick axe..."