Firefly
Disclaimer: I do not own Yu Yu Hakusho.
For the first fourteen years of her life, Keiko's world had been a glass jar. When she was little, she often pressed herself against the walls, dreaming of whatever lay beyond in that unreachable, infinite realm, the birthplace of fairy tales. As the years ticked by, though, she began burning that foolish web of daydreams, devoting herself to making the most of reality. She filled her bookshelves with classic literature and triple-checked her exams before passing them in. In that glass jar, everything was familiar—Yusuke would skip school, Atsuko wouldn't care, Natsuko would order the chocolate cake at the café, the teachers would beam at her achievements, her parents would cheerfully wave at her as she arrived home and climbed the flight of stairs to her room.
Then Yusuke died, the jar shattered, and Keiko couldn't help but cut herself on the pieces. It was all good for Yusuke and even Kuwabara—they were all too eager to explore the world outside; they glowed as if it had been made especially for them, this boundless land of snow. All Keiko felt was cold and dim and lost as Yusuke seemed to fly farther and farther into the blizzard, leaving her behind in the remnants of the world they had grown up in. No matter how hard she tried to catch up, it seemed that the wind would always mercilessly push her back, as if to say, You don't belong here, you weakling, you don't belong here don't belong don't belong don't belong—
And Yusuke's light would blind her and the moon alike until Keiko wanted to scream at her own flickering little glow that could never scare the night, to cry at her inability to ever leave the glass fragments, to slap Yusuke for leaving her stranded there and for never telling her whenever he flew off.
The years ticked by again, and, almost instinctively, Keiko started to rebuild that little glass jar, meticulously gluing the pieces back together one by one. A weak little firefly didn't stand much of a chance against the whims of a snowy village, even if that firefly could slap someone unconscious if provoked. And although she remained unaware of it, she slowly started to glow brightly again, reveling in a good day's hard work and small successes. Once again, she could be sure that Natsuko would order the chocolate cake, that the teachers (though they were different ones now) would beam at her achievements, that her parents would cheerfully wave at her as she arrived home.
On the day that Yusuke came back for her, Keiko would shatter the jar herself this time.
Notes: …That came out quite differently than I expected. I had originally planned for this to be a much needed rewrite of or belated companion fic to my Keiko-defense piece, "Fighter" (which will make your eyes bleed in horror, by the way, it's that bad). Somewhere along the way, it mysteriously turned into YusKei semi-fluff.
In case anyone's curious as to how I came up with the metaphor behind this story, the kanji for Yukimura means snow village, and the kanji for Keiko means firefly child.