The first scene takes place during Legend of Korra (right after Su and her family are rescued, with the first part of the conversation being from that episode). The rest happens after the show ends. Forgive me if I screwed up anything canon, it's been a while since I saw LoK. XD

"Aren't you coming back to Republic City with us, Grandma?" Opal asked hopefully.

"No, my fighting days are over. Don't tell Korra, but my back is killing me now. This is why you didn't see Katara messing with that civil war nonsense. At some point, you gotta leave it to the kids." Waving her hand dismissively, she walked off to gather her things.

"I want to thank you for coming back to save me," Zhi Li said. "And don't be too hard on Bolin for working with Kuvira. His heart was in the right place."

"I think Bolin has worked his way out of the polar bear doghouse," Opal said playfully, kissing him on the cheek.

"Yes!" he exclaimed triumphantly, laughing. Lin just rolled her eyes, only half paying attention. She didn't want to leave things this way with her mother, but she also didn't want an audience for what she had to say.

"We should get going," Zhu Li said. "I'm afraid I have bad news to deliver to Republic City. Kuvira is going to attack in two weeks."

"Oh no..." Opal said, a concerned frown on her face.

Lin sighed heavily, feeling the weight of her responsibilities. "I just need two minutes," she said, going over to her mother who was lingering nearby. "Mom. Can we talk for a second? Alone."

"Oh, alright." They walked a little ways away from the group. "What is it?"

"Why did you answer Bolin when he asked? Why did you tell him?"

"I wasn't telling him. I was telling you. I thought that was obvious."

"The only thing that was obvious was that thirty years of me asking wasn't enough, but apparently some punk kid being nosy was."

"Look, I do realize that maybe it wasn't the best way to go about it. I may be the greatest earthbender of all time, but the interpersonal crap has never been my forte."

"I don't have a lot of time to stand here and chat. Can you just give me a little more? Anything? Who he was, why he left?"

"Fine, but you need to understand that the answers you get might not satisfy you or make you happy."

"Happy..." Lin muttered with a scoff. When was she ever happy? "You know, I'm not an idiot. I figured the reason you kept it secret all these years was to 'protect' me or some bullshit. Not that that's any excuse. You should know by now I'm tough enough to handle it."

Her mother sighed, a complicated look on her face. "Kanto was a man that I was casually involved with for a time. Months, I guess. We weren't in love or any of that nonsense, and we were discreet, so no one really knew about him. With the very public nature of being Chief, I preferred it that way. The less that people knew about my personal life, the more effectively I could do my job. I'm sure you agree."

"What does any of that have to do with not telling me?"

"Nothing. I'm setting the story up."

"Just get on with it," Lin said impatiently. "They're waiting for me."

"I will when you stop interrupting me." Toph took a deep breath and let it out slowly; Lin also took a deep breath, resisting the urge to slap her. "Kanto eventually got fed up with Republic City - and me, I guess. He was an avid traveler and had always come and gone as he pleased, but after one particularly nasty argument, I suspected he wouldn't be back. And I was right. In retrospect, my crazy mood swings were probably part of what chased him off."

"Right. I guess you're talking about me coming into the picture."

"Mhmm. He left about half a year before you shocked everyone with your sudden appearance. Obviously, he didn't know about you."

"Do you think he would have stayed if he had known?"

"I don't know. Maybe. He was a decent person. Not exactly 'dad' material, but he might've stuck around."

"But shouldn't he have heard about me eventually? You've always been pretty famous."

"Who knows? Maybe he assumed there was some other guy."

"So...that's it?" Lin asked, feeling a little let-down.

"What do you want me to say? I never heard from him again and I don't know anything else."

"This isn't exactly a scandalous, life-altering story, Mom. I can't believe you held onto it for so long. Just doesn't make sense. You really thought that would crush me?"

Toph just sighed and lifted her hands, shrugging. "Well?"

The detective in Lin made her suspicious. She had a feeling there was more to it than that, but unfortunately didn't have time to stick around and dig for it. Toph wouldn't give it up easily, she was sure. "Alright," she sighed. "Thanks, I guess. Better than nothing."

Author's note- The rest takes place after Kuvira is defeated.

From her little cave in the swamp, Toph was acutely aware when the bison landed. Once ascertaining the identity of her visitor, she slowly pushed herself to her feet and hung the kettle over the fire. Difficult conversations were always a tiny bit easier with a drink in hand, and this one was sure to be a doozy.

"Mom?" Su called out a few minutes later.

"In here."

Familiar footsteps entered her home. "Hey. Uh, how've you been? I guess you must know we defeated Kuvira."

"Mhmm. Good job. Though I'm not entirely sure what happened. The spiritual energy here went bananas and there was too much interference for me to see a whole lot through the vines."

"Korra accidentally created a new spirit portal in the middle of the city when Kuvira's weapon went off."

What? "Ah. Makes sense." She stoked the fire a little. "So. What brings you to my swamp?"

"Nice to see you, too," Su said dryly.

"Stop trying to guilt me into being sentimental. You didn't come all the way out here just to say hi."

"No, you're right. Actually, I've got a bone to pick with you."

"What have I done, now?" Toph asked with a sigh, though of course, she knew.

"I know you told Lin about her father."

"Ah, I see. So it's your turn now?"

"Well...yea. I mean, why would you tell her if you weren't planning on telling me, too?"

"Maybe I have good reasons for keeping it to myself."

"Wh- Are you- Are you serious right now?" Su spluttered, getting angry. "Bolin - who you had never met before - casually stuck his nose in our family business and you answered the question Lin has been asking you since she could talk. It was the big, huge secret that you refused to discuss, and we find out he was a nobody. There was no scandal, no heartbreaking story. No reason at all to keep it from her, even into adulthood. And now I come all the way here and you're really not going to tell me?"

"C'mon, Su. You're smarter than that. You can't think of any reason for me to have kept Kanto a secret?"

"I've been thinking about it ever since I found out. Nothing makes sense."

"Every action has a consequence," Toph mused, half to herself. "Keeping secrets cost me a lot. Telling them might end up costing more. But I know you're not going to let me off the hook."

"You're right, I'm not."

"It's going to hurt you," she warned. "Are you prepared for that?"

"Well, you seemed to feel the same way about telling Lin and it turned out to be nothing serious. How bad can it be?"

Toph shook her head wearily. "I never worried that Lin would be hurt by knowing the truth."

"Wh- Then why-?"

"It was you I was worried about."

"Huh? How would knowing about Kanto have hurt me?"

"Are you kidding? You two were always jealous of each other, for every little thing. If I cut a chocolate bar in half and one piece was a hair longer than the other, I had to deal with a full-on tantrum."

"But why-" She cut off; Toph could almost hear the gears turning in her mind. "You couldn't tell me...could you? Because whoever he was, he wasn't a nobody like Kanto. He was someone significant. I'm right, aren't I? I'm guessing we're talking about a career-ruining scandal, here?"

Toph let the questions hang in the air. The kettle was ready and she busied herself pouring it, then handed Su a cup and bent herself a little rock stool to sit on. "No scandal. Just a lie that I couldn't take back. To be honest, I was always a little surprised no one figured it out," she mused. "You share a lot of his qualities and mannerisms, despite the fact that he wasn't fully involved in your upbringing."

"Wait. I- I actually knew him?" Su stammered, sounding shocked. "Is he still alive?"

Toph sighed, feeling that old hurt sharply. "I'm afraid he passed away years ago."

After a heavy pause, Su said, "You- You loved him...didn't you?" Toph didn't answer, but she knew her younger daughter was adept at reading people, so she really didn't need to. "Why are you so reluctant to tell me who he was?" Su asked, a pleading note in her voice.

Because I don't want you to hate me. Again. But she couldn't say it aloud.

"Spirits, Mom, it can't be that bad. Just tell me who it is and get it over with."

Toph took a deep breath, and let it out all in a rush. "It was Sokka."

Su's heart skipped a beat. "Wh-" She cut off and it took several seconds for her to speak again. "Why?" she finally choked out.

Toph cocked an eyebrow, confused. "I don't understand the question."

"Um. Why...was it a secret? Why wasn't he more involved? Surely he had to at least suspect I was his?"

"Oh, he sure did. It took some doing, but I was able to convince him that you weren't. Despite the fact that our time together was...unofficial...he wasn't too happy with the idea that I'd been with another man."

"Wait, were you?"

"No. It was a lie."

"But...why? To what end?"

"Lots of reasons. I'd gotten used to being a single parent, with Lin, and I didn't want him interfering in my life and trying to make decisions for us. I didn't want him to pressure me to get married. It never would have worked, and the end result would have been you - and Lin too, by default - splitting your time between two households that were at odds with each other. Lin would have been jealous that you had a dad and she didn't. Everyone would have been stressed out and angry. It wasn't a future I was interested in dealing with. So I did the only thing I could think to do to preserve my independence and my sanity. I lied. And though I didn't deserve it, he trusted me." She found herself a little surprised by how cathartic it felt to finally get this off her chest. However, her next words had to be forced out. "For what it's worth, I do have...some regrets."

"So...he never found out?"

"No. I'm sure he would have kept in touch with you better if he'd known."

"That would have been nice..." Su said softly, angry tears in her voice. "I know we weren't that close, but I still missed him. If I'd known..."

"Now you see why I didn't want to tell you?"

"You had no right to keep it from us! And now he's gone! I'll never get back the time I could have spent with him."

"I already told you I regret it," Toph protested, the guilt peaking. "What more do you want from me?"

"Don't try to tell me I'm not allowed to be angry! I just- I need some time to think." With that, she stalked away, leaving Toph alone once again with her deep regrets.

Spirits, what a mess, Lin mused to herself, surveying the ruined buildings. She was supposed to be on vacation before getting to work on putting Republic City back together, but there was almost as much that needed to be done here in Zaofu. And of course, Su and Opal had mysteriously vanished. Fat lot of help they were.

As if the thought had summoned them, the dripping bison known as Juicy flew overhead and landed out of sight. A few minutes later, Opal found her.

"So you two are back, huh?" Lin said. "What were you doing?"

"Mom wanted to talk to Grandma Toph." There was a faint frown creasing her forehead.

"Ah..." I should have guessed that. "Why do I get the impression it didn't go well?"

"Mom didn't say anything the whole way back, then stalked off to her room. I'm a little worried. Do you think maybe you could try talking to her?"

Lin cocked an eyebrow at her. "What makes you think I'd have better luck than you?"

"I don't know. I guess...it's something you two have in common. You know, 'dad issues.'"

Lin rolled her eyes. "Fine." Despite the reluctance, if she was being honest with herself, she was devilishly curious. Su would probably just tell her to go away and mind her own business, but...couldn't hurt to try, right? As she made her way there, an unexpected memory of her childhood surfaced. As young children, before the teenage years had destroyed what passed for a bond between them, they had shared a room. On many occasions, she had comforted her little sister when their mother wasn't around. Which had been often. "Su?" she called, knocking. "Can I come in?" After a long moment, the lock clicked and the door popped open. Su was sitting on her bed, hugging her knees, eyes red and cheeks wet. "Opal told me you got into it with Mom."

Su frowned. "She said that?"

"Well, those weren't her exact words." She sat down at the foot of the bed and stared at the wall awkwardly, arms crossed stiffly. This wasn't something she was good at. "Anyway. I can guess what it was about."

An irritated noise came from her sister and she glanced over to see a familiar petulant expression. "You just want to know, don't you?" Su asked, her mouth twisting. "You don't actually care about how I feel."

"Look," Lin said with a sigh, a little abashed but not enough to actually admit it. "I'm...glad that the three of us finally got things out in the open and everything's good. Relatively speaking. I honestly can't believe how much the lifetime of family drama has been weighing me down all this time. The last thing I want is for it to go wrong again. I'm probably the only person you can talk to about this stuff, so you're stuck with me. And of course I want to know what she said. How could I not? You know who my dad is. Everybody knows, thanks to Bolin and his big mouth."

"So it's only fair, right?" Su said bitterly, shaking her head.

"You don't want to tell me, fine. I came here because Opal asked me to talk to you. But if you want me to leave, just say the word."

Su didn't say anything for a little while, and they just sat there in tense silence.

"He's dead," she said finally. "And he never even knew he was my father because Mom lied to him. She pushed him away. She made that decision for all of us and stuck with it."

"It's Sokka, isn't it?" Lin blurted, unable to keep the life-long suspicion in any longer.

Su's eyes widened in shock. "How- How did you know?!"

Finally. Confirmation. It was so incredibly satisfying, a weight lifted from her shoulders. "I've always known. Suspected, anyway."

"Wh- Why didn't you ever say anything?!"

"I almost did, once. Don't you remember? Guess you were probably...six or seven?"

"I don't remember."

"We were fighting, probably about something stupid. I just remember wanting to say something really nasty, so I taunted you by saying I knew who your dad was but wasn't going to tell you. Of course, you threw a fit and went crying to Mom, who called my bluff. She just stood there with her arms crossed and challenged me to say who I thought it was. But...I couldn't. I wasn't sure I was right, and I didn't want to look stupid. Plus, I knew she'd just deny it even if I was right. So...I let it go."

"But...how did you know?"

"I walked in on them once."

Su's hand went to her mouth, shock and mild amusement on her face. "Oh, Spirits. But surely you didn't understand at the time? You couldn't have been more than five, assuming this was before I was born."

"Yea, four or five, I guess. And, no, it wasn't until years later that I understood and put two and two together."

"Seems like weak evidence for you to have drawn the conclusion that he was the one. For all you knew, she could have been with other men much more discreetly."

"There was other stuff that made me think it was him. You've always kind of had a Water Tribe look about you, and there's something about the way you bend. You're a lot more fluid than most earthbenders. It's...weird."

"I always thought that was because of Katara." She chuckled suddenly. "I remember watching her and wishing I was a waterbender instead of an earthbender. I'd mimic her movements sometimes. I think it might have influenced my bending."

"It's almost like, deep down, some part of you knew."

"I can't help but wonder if Katara knows the truth. Or suspects, at least," Su mused. "Mom did say I'm a lot like him. Katara would have noticed that, too, right?"

"With that logic, wouldn't he have suspected, himself? In spite of Mom's lie?"

"Maybe he did. Maybe he just kept his distance to avoid drama." Her voice was full of bitterness. "Maybe he wanted to believe the lie because it was easier."

"Oh, quit feeling sorry for yourself. It's not like he wasn't around. At least you got to know your dad, even if you didn't know who he was. I hated knowing. I resented you for being born and having a dad. And when I got older, I resented him for not being a dad when he had the chance, and then for leaving."

"You were grown when he went to the South Pole."

"He and I were really close before you were born," Lin continued as if she hadn't spoken. "Then I barely saw him for...a while. I realize now it was Mom's doing, pushing him away, but at the time, I blamed you."

"Sorry I ruined your life," Su drawled, rolling her eyes.

Lin waved her hand dismissively. "I got over it. I know you probably don't remember, but we were pretty normal sisters for a few years there when you were little. Then puberty hit and I turned into Mom, go figure."

Su threw her head back and laughed. "Spirits, Lin. You've really been doing some introspection, haven't you?"

"Bah. Too many near-death experiences lately. And Mom coming out of the woodwork kind of shook everything up. I didn't have much of a choice."

"Guess we've flipped roles," Su muttered, a grim note in her voice. "You two are on good terms and I'm...I don't even know. I'm so angry, and hurt. She's let me down so many times. Being so busy with her job all the time when we were young. Sending me away when I was just a stupid, naive kid. Barely being around when my kids were growing up. I forgave her for all that a long time ago, but now it's like it's fresh all over again. She actively deprived me of having a father for incredibly selfish reasons. And you know what? She still couldn't bring herself to actually apologize. All she could do was admit she has regrets."

"Please. That is an apology, for Toph Beifong. And you don't want to be like me. You don't want to spend the rest of your life holding a grudge."

"I am many things," Su said with a twisted smile. "'Like you' is not one of them."

"Well, we have one thing in common. Neither of us will ever get any closure with our dads. I guess mine's probably long gone, too."

"I'm-" She cut off, frowning fiercely at her hands in her lap.

"What?"

"I'm...sorry you never got to know him."

Lin shrugged, unwilling to show how much it hurt. "I don't know. Maybe it's better that way. Can't miss someone you never met, right?"

"You can share mine if you like," Su said with a soft smile.

Not exactly a happy ending, but a realistic one. I've always wanted to explore a scenario where Sokka was Su's dad, and this is what I came up with. Hope you all enjoyed my story, and please, please, leave a review with your thoughts! Knowing what works and what doesn't work helps me become a better writer :)