A subtle mien. One of the requirements of the job. The tendency to revel gloomily in the futility of one's task was not a requirement, but he had that too. Unpreposessing, free of any visible noteworthy characteristic whatsoever, he passed unseen through the mass of humanity that was his eternal duty, charge, and source of sustenance.
When that mass inevitably ceased to be, whether through its own destructive whim or a cosmic accident, his task would end in failure. As long as it continued, he could consider himself a temporary success, though he did not think of it that way. Instead he thought almost longingly of the future, in which his failure would precipitate his superfluousness, and thereby his demise. It was hardly a death-wish, he thought, since his was hardly a life. More like looking forward to a particularly final retirement.
He was humanity's guardian angel. Mankind's gentle shepherd. He winced in pained amusement, which was as close as he ever came to laughter. Chancing to pass by a department store display, he caught his reflection in the mirror, and completely failed to recognize himself. His face was that forgettable.
Should he ever have contemplated an end to his isolation, that would have stymied him. How could he form a bond of intimacy if his putative beloved could not even recognize him when they met again? He supposed he could keep her with him always, but even then, she'd wake up next to a stranger. A gloomy enough thought to put a bit more spring in his step, and he continued down the road.
Another hour, another week, another year, another century. Time flowed too slowly to keep his interest in the changes it brought from flagging, but too swiftly to allow him to savor anything before it vanished into history and then oblivion. The invisible wings at his back drooped, making his back ache, too tenuous to fly, too heavy to forget.
Just like everything else. He looked into the night sky from atop a 35 story apartment building, sensing a few thousand of his billions of charges asleep beneath his feet. God might still be up there, but it didn't make a difference to him anymore. If people stopped believing in God, he'd still have to keep them going. He stood up, climbing to the edge of the rooftop and standing with his toes at the very edge, thinking about jumping. Invisible wings spread by instinct. They wouldn't let him fly, but they'd slow his fall. He could not die until the moment after the last human being. He thought about the ways that could happen. War, disease, pollution, maybe an asteroid collision...
One of the stars twinkled. Yes, it would all end, someday. But not tonight.