My memory is kind of fuzzy, but it was either a children’s or young adult novel I read in the early-to-mid 2000s (I’m leaning closer to somewhere around 2004-2006, give or take a year). The main plot line was that there’s some sort of horrible acidic superstorm approaching the house of these kids. Their power goes out, so the older sibling tries to calm the younger ones by telling them a story about fairies. Their parents aren’t there (I think I remember them being out of the house scavenging for resources. The kids are worried about this, and I think it’s implied they might be dead, but I’m not sure). I remember this part of the story being pretty dark.

After this, the story then shifts to the kid’s story, following the exploits of the fairy and its mischief in a much lighter and happier world, while periodically interjecting dialogue between the siblings. I also remember something about an old lady meeting the fairy. I can’t remember the story very well from here, and I don’t think I finished the book.

If it helps, I remember the cover of the book depicting some storm cloud and a lightning bolt, with the title involving something like “Sprite” or “Fairy.”