You're ridiculous.
Sokka happily tugged the letter tied with a blue ribbon out of the stack of dispatches he had been brought today. Pulling the ribbon loose, he opened the letter to see his sister's handwriting, the familiar script from back at the South Pole.
He smiled, abandoning the rest of his correspondence on his desk for later and moving to the couch with his sister's letter.
It was chatty and cheerful, and Sokka grinned at it, feeling a faint pang - he missed Katara; they'd had several years to get used to not being together all the time but they had been their whole lives up until . . . well, right up until a few months after the war had been brought to an end. When Aang finally left Caldera City and Katara went travelling with him on his Avatar duties - and Sokka stayed in the palace with Zuko, taking up official duties of his own here.
And keeping Zuko from going completely insane as he struggled under the weight of his role as Fire Lord, which was more of an unofficial duty Sokka had given himself before he realised. Not that he was unhappy with it. Sokka glanced up from Katara's letter to where Zuko was frowning sternly at a letter bearing an Earth Kingdom seal, taking absent notes without looking.
Sokka shook his head, smiling fondly, and went back to reading.
His breath caught and his fingers tightened on the paper. Katara's handwriting had gone loopier than usual and messy with excitement, but Sokka could still read it fairly easily, and she had just said-
Sokka brought the letter closer as he hurried through the rest of the letter, his breath coming a little too quickly. Katara ended the letter promising to tell him more when they visited next - soon - and telling him not to fuss.
Sokka let out a rough little sound, not quite a laugh, and bit his lip.
"Sokka?" Zuko pushed away from his desk and turned towards Sokka. ". . .what's wrong?"
Sokka shook his head, laughing. "Nothing." he said, waving the letter a little. "My sister, uh-" He sniffled.
Zuko rose, crossing the room towards Sokka. "What's Katara got to say?" he asked, waving a hand as he got close, not quite imperious. Sokka pulled his legs out of the way and Zuko settled on the couch close against his side.
Sokka tilted the face of the letter towards his boyfriend helpfully. "Ah. . . She and Aang, they're getting married." He snorted, grinning. "Well, officially. They're really engaged now." He sniffed again, pushing the letter at Zuko and rubbing his eyes. "I can't believe. . ."
". . .that's good, isn't it?" Zuko said almost tentatively, and Sokka dropped his hands.
"Of course it is!" Sokka said, and then realised Zuko looked confused, rather than dubious or disapproving or anything. "I mean, I've known they'd get married for years, but. . . Yes, this is good news. I just can't believe my baby sister is getting married." he added, with a quiet sniff.
He blinked rapidly but failed to stop a few surprised, overwhelmed tears from escaping him. "It's just. . . I mean, I'm happy, but . . . 'tara's getting married. How is that even. . ." He wiped a drip off the bottom of his chin.
"You're ridiculous." Zuko said, his voice warm, and wrapped an arm around Sokka's shoulders, kissing his wet cheek.
"Shut up." Sokka said, leaning into Zuko. "My baby sister is engaged, I'm allowed to be emotional." Zuko chuckled and Sokka elbowed him. Lightly, because planting an elbow in Zuko's stomach had a roughly similar effect to elbowing someone wearing plate armour - it always hurt you more than him. "And I was surprised."
"Because Katara and Aang, that's a surprise." Zuko said dryly, and Sokka huffed.
"Hey, I practically raised her, even if I know Aang will take good care of her, I'm supposed to be emotional right now." Sokka said, raising his chin and frowning at Zuko.
"Are you sure she didn't raise you?" Zuko teased lightly, rubbing his cupped hand over Sokka's shoulder. "I know she's your baby sister, but. . ."
"Oh. . ." Sokka shoved at Zuko, though not enough to actually push him any further away. Zuko laughed and shifted a little, lounging against the arm of the couch. "Katara might mother everyone, but she was my baby sister, and I did spend . . . most of my life taking care of her." He sighed, mouth twisting, half a smile, though he felt a tinge of sadness at the thought. "Even if she doesn't need me to do that nearly so much now, it's just . . . strange to think of it that way. Letting her go, sort of."
Zuko nodded, lips pursed, watching Sokka, and though certainly he must have been busy he didn't move to get up and return to his desk.
Zuko held out a hand, not quite beckoning, and Sokka smiled a little more and stretched out along Zuko's side, letting their legs twine together. Zuko curled up to him. "Tell me about growing up with your sister?" he invited, and Sokka laughed, but nodded. Zuko stroked up and down his ribs with one hand, propping up enough to watch his face as he spoke.
Because Katara may be solidly the Mom Friend/Team Mom, but Sokka's a pretty protective big brother, too. And even once scattered all over the world . . . they're a close family.