Catastrophes and mysteries

Why tell stories where bad things happen?

I think that in some way, stories are meant to turn us inside out. Regular people going about their lives generally don't reveal their inner hearts, but in stories, we hope to see a glimpse into a character's nature. Regular lives don't have many moments where everything changes, but a good story often does.  In the same way, regular people don't hope for bad things to happen, but they may in their stories. I think a story is like a dream--the more it exposes everything that's normally kept at arm's length, the more work it does.

How does mystery work in UFO in Kushiro?

On one level, mystery propels the plot. We don't know why Komura's wife leaves, so we keep reading in the hope or expectation that more clues will arise. On top of this background mystery, we don't know what's in the box, and again are pulled forward by the desire to know.
But that pull for the reader contrasts with Komura's own nonchalance. He never asks his wife why she's fixated by the earthquake imagery, and he never asks Sasaki what's in the box. How can he be so indifferent? This is how we get to know Komura and his emptiness: through his own immunity to mystery. The unanswered questions address character as well as plot. And they generate a third mystery, the question of what is inside Komura, anyway.