Based on an earlier chapter of the manga that didn't make it into the episodes. Here's a brief overview:

Yusuke is still in limbo with Botan. It's Christmas Eve a popular time for couples to go on dates in Japan, and as they're wandering around they see the fixated ghost of a girl. We never learn her name, but she explains that she's been waiting on this bench since her death last Christmas. She was supposed to meet her boyfriend Kenji there, but she became sick and never got to say goodbye, and feels guilty for making him wait. She hopes that God will let her see Kenji one last time if she stays here until Christmas, so Botan says that they'll wait with her to see if Kenji comes—if he doesn't, the girl will let Botan take her.
Kenji eventually comes, but he's meeting another girl, and the three overhear him explain that his old girlfriend was just someone to kill time with, and that he'd made a bet last year that she'd wait for him for five hours, but she never showed up. The girl begins to cry, and Yusuke gets angry. He tells her to erase the guy from her heart, and when she says that she can't, he decides to make her forget. So, Yusuke dashes off with the fixated ghost for a night on the town.
In the end, she tells Yusuke that she's not mad at Kenji, since because of him, she met Yusuke and had the best night of her life. She lets Botan take her to heaven, and we sit and enjoy a nice fluffy moment… Then Yusuke proceeds to scare the crap out of Kenji—ah, poetic justice.

Unofficially titled Knight in Shining (and Magnificent) Armor, so that it'll be abbreviated to KiSaMA. That's even better than THE (The Heavenly Executioner). Merry Christmas, people…

Disclaimer: YuYu Hakusho belongs to Yoshihiro Togashi

Knight in Shining Armor

At times, if I concentrate hard enough, I can still summon the feel of a winter wind's biting chill upon my face. Relishing the sensation, I let a shiver run through my entire being. What I would give for one single flake of snow, a tangible reminder of everything I once held dear.

Softly the memories filter back, vague images associated with their strangely detached feelings. Muted contentment and gentle awe revel in the harsh and overcast skies, while more stirring emotions cherish the icy air that transforms each breath into a frosty mist.

But the most vivid imprint upon my soul is image of a park bench.

It attracts more memories to it, like moths flocking to a flame, until I recall the reason that this particular reminiscence is so hard to grasp. The recollections of my life are perfectly intact, but this time was shadowed in the hazy veil of death.

The little plaza where the bench was located was familiar enough to me in any season, but I associate it most fondly with winter.

It was the end of December. Crowds rushed past, ebbing and flowing, chattering like the waves upon the shore. Seated, waiting, I drifted among them, content to watch. Mothers turned up their children's collars against the chill, shoppers toted bright bags whose contents were a mystery, and lovers wandered past hand-in-hand.

People had approached me every so often, inquiring as to why I hadn't accepted the inevitable and just succumbed to the inheritance that was mine by right. Behind their hands they whispered fixated soul, lost cause, you have to wait for them to move on their own…However, I had readily accepted the fact that I had died.

Yet I still had something important left to do. Death shouldn't cause one to give up on the living world.

Besides, like a small candle in the darkness, I carried in my heart a tiny flame of faith.

I sheltered a firm belief that if I waited until next Christmas, God would reward my patience, my dedication. I prayed that He would allow me to see Kenji one last time, would give me a change to apologize, to rest in peace. The wait would only make the gift that much more precious, just as the time leading up to the moment of Kenji's arrival, saying "I'm sorry I'm late," made me appreciate every second of our time together.

God answers all prayers, but not always in the way one expects.

That Christmas Eve Kenji came, but not for me. He'd walked straight through me to excuse his customary lack of punctuality to the woman he truly loved, not the 'no one special' he'd toyed with to kill time.

I would have been eternally devastated, if not for one boy.

The traditional romantic hero is pitted against some great force of evil that stands between himself and his soon-to-be true-love-at-first-sight. The antagonist is perhaps a wicked captor of a beautiful young woman, or an unjust standard of society that obstructs their true love. But the handsome gentleman always gracefully triumphs, then proceeds to woo his fair lady with courteous words.

I know of no one who was saved by polite speeches, a gallant attitude, or godlike good looks.

I've seen a hero who rescues a person whether or not they are aware they needed salvation, and even against the victim's will. And, though sometimes unwillingly, that savior acts out of true love— caring for another to the point that they would do anything, no matter the cost, to make that someone happy, to see their smile.

Urameshi Yusuke was a juvenile delinquent, a youth who often acted crude, rude, and socially unacceptable.

He and Botan had waited with me for that final day of my vigil, though he was only there because the ferry girl had made him stay with her. When Kenji broke through all the oblivious delusions about our relationship, the dark haired boy snapped. At my tears, he jumped into the kind of action that is what truly saves people.

Yusuke demanded that I erase the unfaithful man from my heart, to waste not one more thought on a person who wasn't worth my time. But I wasn't ready to give up on my devotion, to let my compassion go.

Incensed, he took my arm and forcibly pulled me away from the park bench, from what had been the symbol of my final desire in death.

Now, I smile fondly on his recklessness. He hadn't been angry at me, at my stubbornness. His anger at Kenji's unfaithfulness had been a spark, and it lit a fire fueled by passion. It wasn't a romantic love, but then again I don't believe he'd have made a good, sensitive romantic anyway.

That night, Yusuke had filled my mind, heart, and soul with what must have been a lifetime of dates all condensed into a matter of hours. The essential part of me that Kenji had destroyed, my savior fought for with all his strength.

As we looked down upon the city's lights in the dark night, high above like a pair of twin stars, I had tried to express to him what it had meant to me. He'd shrugged it off, more because I had told him that I was grateful to have met him and had the best time of my existence, rather than his inability to understand that as my reasoning to forgive and give my best wishes to my once-upon-a-time boyfriend. However, when I see him again… I'll tell him what I didn't say.

I never told him it was Christmas.

He knew what night it was, but he would have only recognized it as a holiday for lovers, a night for couples on dates.

But what I didn't tell you, Urameshi Yusuke, is that Christmas celebrates a savior.

It celebrates the birth of a baby who would one day grow up to love the world unconditionally until his death, and he died because of it. You didn't die for me, but I am no less grateful because of it. I could even call you my angel, a fulfillment of God's answer to a prayer.

Salvation doesn't dress in shining armor.

…
Owari
…

-Windswift Shinju