Quick note on the characters' living spaces: my headcanon is that Tamaki eventually moves in with Haruhi, and Kyoya takes his old apartment. Honey and Mori take a room above Haruhi and Tamaki; the twins, one above Kyoya. I don't know if that fits with the building Haruhi and Tamaki canonically live in, but if so... too bad, haha!
"Kyoya!" Tamaki exclaimed as he entered his friend's apartment.
Kyoya eyed the other boy a bit warily. "What is it?" he asked, not yet lowering the newspaper he held in front of him, as if to shield himself from Tamaki's latest flight of fancy, whatever it could be.
"Do you know what this place is missing? This whole country?" Tamaki demanded, his eyes glittering with excitement. Kyoya cringed, already knowing what was coming.
"A kotatsu!" Tamaki finished triumphantly. "I only got to sit at yours a couple of times. Wouldn't it be nice to have one here?"
"Why don't you ask Haruhi about getting one?" Kyoya asked, his tone so even that he seemed bored.
"I already did, but she said we can't get one because there's not enough space!" Tamaki wailed.
With an aggrieved sigh, Kyoya finally let his paper fall to his lap. "I barely have any more space than you and she have," he countered.
"I know," Tamaki replied, widening his eyes in his pleading lost-puppy expression, "but think about how much more you could use it! Haruhi is always busy with her schoolwork, but you could have everyone over to eat and —"
"I'm not going to cook for you," Kyoya said bluntly as he slid his glasses up the bridge of his nose. "And I won't order catering for you, either," he hastily added, anticipating Tamaki's next request.
Tamaki's mouth twitched, as if he were about to start blubbering. "All right," he said. "I'll just go then." But rather than leave, he scooted into a corner to pout.
"You can stay there as long as you like," Kyoya said calmly, again raising his newspaper to eye level "I'm not going to change my mind."
"Then I guess I'll just stay here forever," Tamaki replied sadly.
"Haruhi would miss you," Kyoya said off-handedly.
Tamaki made a fake sniffle. "No, she wouldn't. She wouldn't even realize I was gone."
Kyoya rolled his eyes. Tamaki can certainly be persistent in faking upset, he thought. "Fine, Tamaki," he said. "If you're just going to be contrary, I'm not going to argue with you. Haruhi will just have to come over and drag you out of the corner herself."
"She can't do that," Tamaki said. "She has class all day today," he explained, seemingly forgetting that he'd just insisted Haruhi didn't care about him enough to even consider finding him.
"Uh-huh," Kyoya lazily acknowledged as he turned the page. "It would certainly put her out. Disrupt the studies she came all the way here for."
A strange look came over Tamaki's face, then he sprang up. "Don't worry, Haruhi!" he cried, as if she were in the room, rather than a law classroom a mile away. "I won't do that to you! I can pull myself together from this disappointment, just for your sake!" Without a further word to Kyoya, he hurried across the room and back through the door into his and Haruhi's own apartment.
Kyoya smiled to himself at Tamaki's typical overreaction. Wouldn't he be surprised, Kyoya reflected, when the kotatsu Haruhi had ordered arrived on their doorstep?