This is canon-compliant with what we know up to season 2 of Korra and the comics The Promise and The Search. This'll probably be thoroughly jossed at some point in the future, but I wanted to explore 1) how the Fire Nation and family would handle having a nonbender at its helm, and 2) the Gaang post-finale.

This started out focusing fairly strongly on Ursa and her family, but it's branched out a lot more to explore each individual POV character and their motivations/lives/relationships. Several particular chapters that can be read as stand-alones: Kiyi (4), Aang (5), Kya (10), Toph (11), Bumi (13), and Sokka (14). However, the story as a whole traces Ursa's life, albeit seen through the eyes of other characters.

Book I: Family

Chapter 1: First Impressions (Katara)

The labor is long and painful, and by the time the baby is finally born, Mai's rain of curses on Zuko, pregnancy, and children in general have dwindled to boneless whimpers of pain. There's a vulnerability on the Fire Lady's face that Katara's never seen before, and she hurries to stop the bleeding before it gets worse. Mai's eyes flutter shut after a while, and it's only her shallow breathing that tells Katara that she's still alive.

As Katara works, the newborn baby announces its indignation at the arrival with a wordless wail. Katara hands the child to the care of her assistants as she heals Mai, but Mai fights her way out of her stupor at the sound of her child's cry. "How is it?" Mai says, struggling to sit up. "I can hear crying, why is it crying—"

"Hold still!" Katara orders, pushing her back onto the covers. Mai struggles weakly, but after more than a full day of labor, there's not much strength left in her. "The baby's crying because it's healthy," Katara says, making her voice as soothing as possible. "And you're not at this point, so you have to stay still until I'm done here."

Mai mutters something under her breath, and her fingers tap restlessly on the covers. Katara thinks that it's a good thing there's no room for knives under a birthing robe, not that Mai has much energy to aim accurately at this point. As she works, the baby's wails eventually die to small, sleepy gurgles as the attendants clean it and swaddle it in a blanket.

When she finally stands up, Mai appears to be getting some much-needed sleep. Katara washes her hands and takes the baby from the attendant, peering down at the small bundle. "It's a girl," the attendant whispers to her.

"I can hear you talking," Mai says hoarsely, startling them all.

Katara smiles reassuringly at Mai, who gives her a bloodshot glare in return. "She's a beautiful girl," Katara says as she places the baby carefully in Mai's arms. "Healthy as an ostrich horse."

"She better be, after all that trouble," Mai mutters weakly, but there's no true venom in her voice as she gazes down at her daughter. There's a moment of silence, and then Mai runs a gentle finger down the baby's cheeks. "Shh," Mai says in a soft, wondering voice. "I'm here. Hey, little one."

There's a tenderness to her voice that Katara only ever hears when she's talking to Zuko. Katara smiles down at mother and child, the two of them lost in their own little world. Quietly, she bundles up her midwife supplies and tactfully leaves the room, ushering the assistants out with her. Mai doesn't look up as she leaves, still murmuring quietly to the crying child.

Katara doesn't make it two steps down the hallway before Zuko descends upon her like a wrathful fire god, his eyes wild. He looks as if he's been pacing out in the corridor for the entire labor, which he probably has. "How did it go?" he demands, and there's a definite hint of frenzy in his voice. "She was yelling for hours about how she hated me, and then she stopped yelling for a long time, and then there was crying, and then—"

Fatherhood's going to be great for him, Katara thinks as she surveys Zuko. It's been barely hours since his daughter was born, and he's already a mess. He clearly hasn't slept, and she doubts that he's eaten, either. His eyes—well, his good one, at least—is wide with terror, and his hair, loose from its formal topknot, is even more disarrayed than usual as if he's been running his fingers through it repeatedly. She places a hand on his shoulder. "Relax," she says, using her best "placating the frantic father" voice. "The birth wasn't an easy one, but Mai's fine now. The baby's a healthy girl." She gives him a smile that's meant to reassure. "You asked for the best midwife, and you got me. Of course everything's all right."

He looks down at her, blinking rapidly. "They're really all right?" he says at last, his voice surprisingly small.

"Yes," Katara sighs. She pushes him in the direction of the door. "Go on. Talk to her."

Zuko takes a deep breath. His chin goes up, and she can almost see him mentally donning the Fire Lord persona as he pushes open the door. The door swings closed behind him, and Katara—even though she really shouldn't, but she can't resist—listens against the door for a few moments.

There's no yelling from mother, father, or child. Smiling to herself, Katara heads back to the guest quarters to wash up.

The announcements go out the next morning: bright, joyful proclamations of a festival to celebrate the birth of Fire Princess Ursa, the future of the Fire Nation. Despite that, or because of that, Katara doesn't see Zuko again until the afternoon. He looks up at her and smiles in his awkward way as she enters his office. He's dressed in his formal Fire Lord robes, looking exhausted but dazedly happy. "Well?" she asks, arching an eyebrow.

He laughs, a soft raspy sound. "They're both fine. Ursa stopped crying after a little while. And Mai doesn't hate me."

"Never thought she would," Katara says breezily. "Trust me, I've said far worse when I was giving birth to Bumi and Kya. It's sort of on par for the course. Still married to Aang, you'll note."

"I can't believe you had two," Zuko says, shaking his head. "Mai said that if we wanted another child, I could be the one to give birth." He looks at her, the levity fading from his face. "Is she really all right?"

Katara looks at him, her expression turning equally serious. "I don't think Mai would survive another child," she says, wanting to press the point home. "This labor was very hard for her, Zuko. If I hadn't been there…"

She can see Zuko freeze for a moment, running the angles and possibilities through his head. He's become better at planning since their early travels together, part and parcel of becoming Fire Lord. Whatever the sum of the calculations, he eventually nods, his jaw setting in determination. "We don't need another child," he says, his voice firm. "Ursa will be good enough for ten."

Katara smiles at him. "That's sweet."

He gives a half-shrug, a flush of color creeping into his cheeks. "It's true."

She pats on him on the shoulder. "Well, just wait until they start growing up," she says wryly. "It only gets harder from here, you know." She shifts a case of scrolls carefully out of the way and sits down on the edge of his desk. "You sound ready for the job, though." He doesn't say anything for a moment, and she leans forward, concerned. "Zuko? What's wrong?"

He looks down. "I want to be," he says at last, his voice quiet. "I just—my family doesn't really have a history of being great fathers, you know?" He raises his head, but his gaze is suddenly awkward, sliding away from her face. "I mean, there's Fa—Ozai—and you can see how Azula and I turned out. Grandfather Azulon wasn't exactly a paragon of fatherhood or grandfatherhood, and then Sozin before him..." His eyes flash to her face, and there's the terror back again, bone-deep. "What if I hurt her? I would never burn her, but what if I get angry or she hates me or she runs away or—"

She places a finger across his lips, stopping his tirade. He almost goes cross-eyed trying to track her finger. "Hey," Katara says firmly. "You are not your father. If nothing else over these past eight years, you've established that and more. And you've learned from him and all his mistakes. Right?" she asks. He nods slowly as if he's processing her words. She waits a moment before continuing, gentling her voice. "I know you, Zuko," she says. "You protect those you care about, and you never, ever give up. You'll stand by Ursa just as you've stood by us and the Fire Nation, and nothing's ever going to change the fact that you love her."

He lets out a shaky breath as she lifts her hand away. "Right," he says. He swallows hard, and his eyes pinch shut briefly. When they open again, they blaze bright with determination, his gaze resolute. "I'm going to be the best father I can be," he says, and it sounds almost like a vow.

"That's the Zuko I know," Katara says with a grin.

He gives a tired laugh and moves to rub his hands through his hair before stopping as if remembering that he has the topknot in. "Right," he says. He pinches the bridge of his nose instead. "Thank you for agreeing to come, Katara," he says after a moment. "I don't know how I would've managed without you."

Katara shrugs. "It was the least I could do," she says, waving a hand dismissively. "And we all agreed that it was time that Kya and Bumi visited the Fire Nation, anyway."

He smiles. "I'm sure Aang has his hands full watching the two of them," he says. "Hopefully they haven't torn up my city yet."

She laughs. "You'd think they were both benders, with the amount of havoc they cause!" she says. "But Aang can manage without me for a couple of days. We'll even wrangle them both into formal wear for Ursa's celebration party. Maybe I'll even get Aang to give a speech about the harmony and prosperity of the Fire Nation or something."

Zuko nods and squeezes her hand, the motion quick and grateful for far more than a simple speech. "I'll see you there," he says.

The worry doesn't quite fade from his face, but steely determination underlines it. On an impulse, she gives him a hug, which, after a surprised moment, he returns. "You can prepare all you want for parenthood, but you never know how good you'll be until it happens," she says softly as she lets him go. "I know that you'll do fine, Zuko. You and Mai both."