Note: This is based on the cannon of the novels (including the "Beyond" chapters), but I wouldn't say there are any major spoilers for those chapters. So if you've only finished the anime, or haven't read the extra novel chapters, don't worry!
A light, dusty snow drifted weightlessly through the grey skies outside his window. Shion's work rested forgotten on the desk in front of him as he tilted his head to stare aimlessly out to the horizon. Only six years before, his vision would have been obstructed by the towering metal walls that enclosed the old No.6.
Six years. Shion sighed. It's been six years since I've seen him.
Of course, it had been an eventful six years. The No.6 outside his window resembled that No.6 only in name. The walls had come down. The people were given their freedoms back. The districts of the city were all given protection under the law, including the West Block. It wasn't without its flaws – people didn't easily give up the lives of luxury they had been accustomed to – but in general Shion felt a lot of progress had been made.
But still...
Still, there was something empty about all of it. He had a satisfying life and was constantly being praised for his efforts within the Restructural Committee, but his mind was often somewhere else. He would remember. It was times like this when a thought would float up into his mind, despite his best efforts to bury it: I need you, Nezumi.
It was defeating and frustrating. He had worked so hard to become strong enough to stand alone, strong enough that he would never become a burden to Nezumi. But when he was lost in thought, it would come sneaking back. I need you, Nezumi.
It was at that moment that Shion realized he had thrown the window open, the breeze that rushed in sending paperwork flying. Just like when we were twelve, he thought, and immediately felt silly for making the association. He sighed again, and closed the window.
Cheep cheep.
"Nezumi?" he cried, as a mouse leapt from the windowsill to land atop the disarray of his desk. It dropped a small capsule in front of it before turning to stare intently at the muffin Shion had been eating before getting distracted. He tore off a piece for the mouse and turned his attention to the capsule, opening it and unfurling the rolled strip of paper inside with shaking hands.
"Shion. It's been a while. - Nezumi"
"'Been a while', he says." Shion scoffed at the note and wondered why his vision was getting blurry. A droplet fell from his eyelashes and hit the paper, obscuring the letters. Tears? He wiped his eyes, grabbed a pen, and tore a strip of paper from his notepad with an air like the world depended on his reply.
"Where are you? Are you coming back?"
He read what he had written, and with a dissatisfied grunt, dropped the paper into the trashcan.
"I've missed you."
That note joined the first in the trash.
"6 years is a long time. I want to write more. - Shion"
Shion grinned smugly and placed this note into the capsule. "Make sure he sends a reply," he said to the mouse, scratching lightly between its ears. "He didn't name you, did he? I'll have to think of one," he mused, setting the animal down and watching as it scurried away.
The mouse came again after two days that felt like an eternity, this time to Karan's bakery. It somersaulted past Shion's feet and stared wide-eyed at the baked goods in the display case. Shion gleefully picked it up and fed it some of his mother's bread before noticing the tiny bag strapped to its back. He unfastened it and pulled out a roll of paper slightly larger than what they had used before.
"Here you go, Your Majesty.
3 lines will have to be sufficient.
This guy is small. - Nezumi"
A smile brighter than he had smiled in several years spread across his face, and he immediately went to work writing his reply.
"His name is Puck, because I think
he seems to have a mischievous quality.
He certainly loves bread. - Shion"
"Do you like that name?" Shion asked, grinning. Puck squeaked excitedly and ran up Shion's arm, curling up on his shoulder. Shion thought of that underground room full of books.
Puck appeared much sooner this time, bounding energetically into Shion's office at the Restructural Committee the following morning.
"Stop naming the mice.
You know you really are an airhead.
Time hasn't changed you at all. - Nezumi"
Shion laughed until tears formed in his eyes, remembering his days with Nezumi in the West Block. Things had been hard then, but he had been truly happy.
Change.
He remembered Nezumi's words from when they were underneath the correctional facility. "I want you to stay as you are, Shion." Suddenly the tears of laughter in his eyes took on a bitter feeling.
Puck cheeped and ran in circles around the pad of paper on his desk, as if urging Shion to write. He took a deep breath and closed his eyes, allowing the rush of emotion to pass. Emotion he would have never known he was capable of experiencing if Nezumi hadn't shown him. He picked up a pen and began:
"I think about you all the time.
I've really missed you these past 6 years."
He paused his writing, considering the gravity of what he planned to write next. Is this really ok? Was he just being naive? An "airhead"? Was that even a bad thing? He inhaled slowly as if bracing himself for an impact and finished his letter:
"I love you."
Nezumi clutched the note tightly in his hand. He had been standing there for nearly ten minutes, reading Shion's words over and over.
"I think about you all the time.
I've really missed you these past 6 years.
I love you. - Shion"
His hands shook slightly as he gripped the paper tighter. "How am I supposed to reply to this?" he demanded, though there was no one around to hear.
He had returned a week before to the nearly unrecognizable West Block – the bazaar had become a nice market with shops selling fresh foods and inexpensive goods, and the residents were living not in ruins but in modest but respectable homes. One section had been turned into a park, and it was there he found the one thing that remained unchanged. Hidden behind trees, he found the entranceway to that room, appearing untouched since those days when he lived there with Shion. Inside, everything was covered in a layer of dust, and there was a note pinned to the wall: "I made sure your books were still here for you."
If he was honest with himself, he missed Shion terribly during the six years he had been away. But there, in that room, was where the pain he had felt being apart from Shion really hit him.
"I love you."
I love you too, Shion.
Nezumi sighed in spite of himself, staring off into the skyline of No.6 and clutching Shion's note tightly. A soft breeze carried the gently falling snow in the direction of the city as if beckoning him. Perhaps he had wandered for long enough.