As pollution gets worse, the upper classes take to the skies, abandoning those who can't afford to live on skylands to their fate. It's not a terrible fate, all things considered. You have to wear a gas mask all the time, and you don't really see the sun any more. The only really weird thing is that ghasts start popping up. They come from negative emotions, the officials say. Well we can't very well just stop feeling now, can we? In the end, it turns out being haunted isn't so different from getting mice. You call pest control and you move on.
Tae has been working in ghast control since his teen years. He could be better with people, but he's good at his job. It's just- why doesn't he exterminate the ghast that's haunting him?