A/N: Warning: Incest.

Acid

"My life ended the day you were born."
- Bellamy Blake, The 100 -

"See, this is what you're going to sound like," Azula purrs, her legs kicked up on the arm of the sofa, reclining as she enjoys Zuko's flag red face. "Oh, daddy, Azula's making fun of me. Azula says I have no friends and am bad at firebending. To which his disappointment in you will grow even more, which is impressive. That level of parental disappointment simply does not exist, but he will reach it."

Zuko rubs his temples. He has been dealing with this for over an hour now. Their father told them to wait in the parlor so he could speak with them about the Day of Black Sun, but he is forty minutes late and Zuko is wondering if he simply forgot, or if perhaps he was assassinated or worse ─ the Avatar showed up.

"I'm not going to tell on you," Zuko groans, unsure how else to respond to that.

"I wonder why father is so late," Azula says slowly with a wicked little smirk on her lips and Zuko hopes it is going to turn into conversation. "Maybe we should check on him."

"You go do that," Zuko replies, waving his hand towards the door. It is not that he dislikes Azula, it is that she makes herself very difficult to like.

"Maybe something exciting happened... Maybe he found the Avatar," Azula says and at that, Zuko throws himself across the room, to her scream of shock, and he pulls her to the floor.

Azula knees him in the stomach as he tries to pin her. He falls from the force, his back slamming against the antique sofa. Her hands light up and he grabs one of her wrists, causing the flames to fizzle out. Her hand clasps onto his, binding it in place, and she leaps up, throwing him to the floor.

She sets her foot on his neck but he breathes fire. A last minute block that Azula is sure even her weakest trainers would be ashamed of is all she can do to keep from being burned. He pushes himself up in her moment of imbalance and she grabs him by the arm, twisting him around and pinning him to the coffee table.

"Give me one reason why I shouldn't kill you right now," Azula says, sounding... livid yet calm. Zuko can feel the flame from her fingertips on the back of his neck, and he is trying to figure out a way to throw her off of him.

"Because father would kill you," Zuko breathes, realizing that the fire has not gone out and he is no longer sure if they are playing.

Azula is unpredictable. One moment she is attempting murder, the next she has having a moment of compassion and risking her own status with father to bring him home and restore his honor. One moment she is fondly remembering their childhood years before time and the man who conceived them tore them apart, the next she is making cruel remarks. One moment she tries to help him fit back in, the next she taunts him about the Avatar.

"Right, right, you're dead in this scenario, so he has no other viable heir but me. He's really going to kill or banish me.I'm so scared," Azula says smoothly and Zuko punches his elbow backwards into her ribs. He pins her to the wall and she just laughs. He can feel her shaking against him as she seems to find it absolutely hilarious.

"And if I kill you?" Zuko cannot make it sound as convincing as she can.

"You couldn't kill someone, ZuZu. Not even me," Azula says softly, watching his stance weaken. "I can see it in your eyes."

She remains there for a moment, her back against the wall and one of his hands on her neck. His foot twitches slightly, waiting for the attack, the lightning or some kind of tackle.

But she touches her lips to his. He pauses, startled. Zuko has only ever kissed one person, and in his confusion and inability to move, she presses harder and Zuko finds himself closing his eyes before remembering himself and pushing away from her.

Azula touches her lips and snaps, "Why did you kiss me, you sick pervert?"

"I-I, you kissed me, Azula!" Zuko has no clue what he is supposed to do. Adrenaline surges through him as the unwelcome heat fades, and he can see the same in Azula.

"That's not how I remember it," Azula says, her words icy and malicious but her eyes as confused as his.

"Don't tell anyone!" is all Zuko can manage to stammer out.

"Don't give me a reason to!" Azula replies sharply, her cheeks a flushed shade Zuko did not think he would ever see.

"I won't," Zuko says as he realizes that Azula now has an unhealthy amount of power over him. One word of this could end Zuko's life, or worse. And Azula cannot be trusted with power like that. If his father knew, he would torture and kill Zuko, period.

She vanishes like a ghost, forgetting entirely about their meeting about their father.

Zuko is in a panic. This kiss that should never have been is going to be the death of him.

[X]

Zuko is woken by knocking on his door. He first thinks it is his uncle waking him up for the day, as he always did. Zuko never woke himself up in the morning; in fact, he never learned how. But it is the dead of the night, the pale moonlight shining through the sheer red curtains, and he is in this cold palace.

He gets up, rubbing his eyes, and walks to the door, rubbing his eyes. To his shock, Azula is standing on the other side, looking strange. She has a freshly blossoming bruise on her neck and he does not think he should point it out. It looks like fingers were on her neck and he thinks for a moment somebody hurt her, but that would be impossible.

"Let me in," is all Azula says. Zuko steps back and lets her inside. He does not move as she mimes hitting him with lightning and rolls her eyes. "Bam, you're dead. Don't just let people into your bedroom without questioning them."

"I... you asked to come in," Zuko says exasperatedly, his head sore. Azula shrugs with a small blink and a haughty contortion of her rosy lips. The lips that kissed his earlier.

"Don't tell anyone I kissed you. You understand me? Father would kill you."

"I didn't know you cared about my life so much," Zuko says sharply and Azula shrugs again. "Are you hurt? You look hurt."

She is stunned that he would even ask that.

When Azula was a baby, Zuko's mother asked him to hold her. He thinks if it were the other way around, he would not have survived because Azula likely would have tossed him onto the floor. His mother handed him Azula to hold and said that she was his sister and she was his responsibility.

Ursa said that if anything ever happened to her, Zuko had to protect Azula, or something along those lines.

Zuko took those words very seriously.

But there are some foes Zuko cannot stand against, even with so much on the line.

"I'm not hurt. I can take care of myself and no one would ever hurt me because everyone loves me," Azula says and Zuko thinks she is protesting too much. But he seals his lips; he does not want to get into a fight with her while he is only wearing his underwear and the palace is deserted save for them and their father.

"What do you need?" Zuko asks quietly and Azula looks him up and down.

She seems to be thinking for a moment. He genuinely does not like that look; it makes him nervous.

Her fingers slide up slowly over herself and he has no idea what is happening for a moment. Why would he guess what is happening?

She slides her thumb under the shoulder of her shining silk robe.

With a single motion, it falls off of her, leaving her naked and exposed.

[X]

One week later, Zuko finds himself in his sister's bed, the shadows of the night shrouding them. It is wrong, maybe. Maybe. Yes, definitely. It has become something they both do without thinking, without knowing why they desire it. But they do, maybe. Yes, definitely.

He is inside of her, thrusting, reaching a climax, when she says, "Stop," and Zuko feels a flicker of hot acidic panic in his chest. He complies, of course, not wanting to have his eyes gouged out. Or having this secret revealed, which would likely come with a worse punishment. "Okay, keep going."

Zuko does not comply this time. "Why did you ask me to stop?"

"I wanted to see if you would. Why else?" she says as if it is so obvious.

"That's..." Zuko ignores it. She is weird. She is incredibly weird and he is okay with it.

[X]

Zuko and Azula's relationship has been going on for too long. Zuko cannot handle it anymore. He simply cannot and there is no escaping. It is impossible to look Mai in the eye; it is harder to look Azula in the eye.

"This needs to end. We need to break it off now," Zuko announces on Ember Island. He is outside in the cold, the rank smell of beach in his nose and the peaceful sound of waves in his ears. The stars are out, missing the sun, missing the sun. Azula has approached him from behind and he does not know what she wants, but he does not want it.

"You think? You really struggle with certainty. And confidence. And, most things actually. You're a struggler," Azula says with a small smirk. She looks amused by his internal torment, or as if she does not believe he could cut the sexual ties.

"Azula, it's killing me." He feels a deep, stabbing pain in his heart when he looks at her. He thinks that he is why she looks so disheveled. Why she is gradually disappearing.

Silence. "That's not a horrible way to die. I can think of much worse things that could be killing you."

She kisses him. This kiss is different than the first. It is harder, more certain, and even more unwelcome, somehow.

He pushes on her shoulder and she looks like she is going to hit him for a moment. This could not be more confusing, and Zuko does not know what he is supposed to do.

"What? Fine. You're so unhappy with this, I..." She does not seem to know what to say. Zuko has never seen her speechless, and she is not for long. "You have no idea what it's like to have something killing you. And I think you're going to find out."

She storms away before he can try to explain himself. But Zuko does not know if he would be capable of explaining himself if he tried.

[X]

That evening, Zuko is curled up with Mai and she is pretending not to notice how oddly he is behaving. But then it comes out of him, as she expected.

"Mai, I need your help," Zuko asks, rubbing his neck. He knows he should not tell, but Azula has avoided him for the remainder of their stay on Ember Island. Her parting words about wanting to hurt him are now getting progressively more concerning.

"Yup," Mai responds, not expending many words over this. It is hot, dry and disgusting on this dreadful island.

"I think Azula is going to blackmail me." It seems to take as much breath as scaling a wall to say those words.

"You're screwed," Mai says teasingly before seeing how grave Zuko's expression is. "How bad is it? What has she got on you?"

Zuko freezes there. He does not know how to voice what is happening. There are no good words for it.

"She kissed me."

"Mhm." Mai just shrugs.

"That's not shocking to you?" Zuko demands and Mai just shrugs.

"Not that surprising. The sexual tension is enough to burn down the palace," Mai says mockingly and Zuko wrinkles his nose in disgust.

"She's my sister!"

But Mai just rolls her amber eyes. "You're the one who kissed her."

"She kissed me," Zuko snaps and Mai shrugs.

"That's not what she's going to say." Mai looks at him as if this is a joke and it makes him sick.

"I've slept with her." That takes as much breath as climbing a mountain in one spurt.

Suddenly, Mai's small smile is gone, her eyes wide. "That is a little more serious."

"I can't even look at her anymore." Zuko takes a deep breath. "I'm sorry to you. And I'm sorry to her and I don't know how to get out of this."

"Having sex with your sister; how could that have gone wrong?" Mai tries to laugh but cannot. This is much more serious. "I have no idea what you're supposed to do about that."

She sounds calm and it enrages Zuko. He knows she is incapable of expressing strong emotion even if she feels it, but he has no words. None at all.

"I'm going to try to talk to her," Zuko says and Mai clenches her jaw, restraining herself.

He needs to do it, even if it is going to blow up in his face. Like everything does.

[X]

They arrive back in Caldera without further incident. Azula avoids Zuko further. He knocks on her door and she does not answer, but he knows that she is inside.

"Azula, please open your door," Zuko sighs, leaning his head against the deep red wood.

"I thought you were done with this," Azula's disembodied voice says sharply. Zuko groans.

"I don't want to do that. I want to talk to you. I want to make this right."

Silence. He thinks at first that he has made some progress, but he does not get a response.

He rattles the doorknob in frustration.

Silence. Zuko grits his teeth and walks away.

[X]

"I'm assuming it went terribly with Azula," Mai says, still sounding so unnerved by it all. "What did she say that makes you think she's going to blackmail you?"

"She said, 'You have no idea what it's like to have something killing you. And I think you're going to find out' and then walked away," Zuko says and Mai squints. The comment is incredibly cryptic.

"Yeah, I've got nothing," Mai admits with a shrug. "Look, if she starts blackmailing you, I'll try to help. I don't think there's anything you can do. You probably should've said no when she first tried to have sex with you. Given that she's your sister."

"I don't know what to do." Zuko looks on the verge of tears and Mai becomes more concerned.

"I don't either," Mai whispers hesitantly. She does not know what else to say.

[X]

Azula is lying in the courtyard, her back on the damp grass as stares at the stars. She did her sunset training and now lies on the drying grass and stares at the night sky. She always found it incredibly beautiful, and this is her favorite place to be.

It is a pleasant kind of exhaustion, the post-training burn. And she lies, basking in it as she basks in moonlight.

The Invasion is tomorrow, and Azula is glad to be tired. That way she cannot be preoccupied with what is to come.

Someone walks up behind her and she is startled. Usually she finds herself alone.

"Can I join you?" Zuko.

"Only if you keep your mouth shut," Azula replies.

He lies down beside her, gazing at the sky. "What are you looking at?"

"You joining me only had one condition, brother." But Azula's lips twitch with a small smirk.

"Sorry," Zuko says with a small laugh.

She presses her lips against his.

They are together in the night.

This kiss is worth it. And what comes next is worth it too.

[X]

Zuko is gone. Zuko is gone and he left her and she has never been so angry in her life. Zuko betrayed her and she feels stupid for not expecting it. Zuko betrayed her and Azula wants to kill him almost as much as she wants to kiss him.

"I want you to kill your brother," father says and Azula does not know what else to say other than to nod.

Ozai watches the pain in her face and does not know what he should say to that.

"I would love to," Azula says, clueless as to if it is a lie or not. "You don't know how much I would love to."

"Why are you so sad he's gone? Have you gone soft for him?" father demands and Azula slowly shakes her head.

"I didn't expect it, is all," Azula says softly. She also did not expect her father to burn her shoulders because she told him the Avatar was dead. But she does expect him to wrap his arm around her because he feels so guilty for watching blood pour down her back like a waterfall.

"I didn't either," Ozai admits, rubbing her arm.

It is the first betrayal in the chain.

[X]

"You left, is what you did!" is the only coherent thing Azula screams at Zuko. "You never cared enough to stay!"

Her lucid accusation feels like acid eating away at Zuko. It burns and bubbles and blisters.

Zuko is taken aback by the shift from ravings to honesty. It is the seventh visit he has made to the asylum, and the first in which she has not tried to murder him. But he keeps coming back because of guilt. Guilt, endless guilt.

"I cared," Zuko says and Azula laughs mirthlessly.

Silence.

"No you didn't. Nobody ever did," Azula says slowly, clearly. The lucidity makes Zuko nervous. "I don't want you to come back here. You made your choice during the comet."

"You know why I left?" Zuko snaps, not sure why he is bristling so much. "Because my life ended the day you were born!"

Azula averts her eyes.

Zuko leaves again.

[X]

Zuko has seen tortured souls in his life. But nothing like that. Nothing like that.

He does not know why he has not done anything to help her. She lies on her bed, chained, and stares at the ceiling. Zuko has captured her after she got into an altercation in a city, four years after running away. And now he has her home and does not know what to do about it.

"Fuck you," is all Azula says. She does not try to escape her handcuffs and that worries Zuko.

He has not seen her in four years. Four years since she abandoned him. For good reason, he supposes. The longer he looked for Azula, the more he realized how much he felt to blame for her mental breakdown. Or the more he felt guilt for using her as a stepping stone to get his mother.

"Listen to me," Zuko says and Azula pointedly looks disinterested. But he knows that she is listening. "I told you that my life ended the day you were born. The truth is, it didn't start until then."

Azula's silence burns like acid.

[X]

One day at a time. They take it one day at a time. Zuko tries to help her; he does whatever it takes. Azula appreciates it, although she would rather have her fingernails pulled out one by one than to admit that.

"Do you want to eat dinner with me?" Zuko asks it every night. Azula has never once said yes. She eats in her room if she eats at all.

"Okay." Pause. "Help me get dressed."

"You know how to dress yourself," Zuko says, taking a subconscious step back.

"The reason you're so afraid is because you know that you want to," Azula says softly, looking entertained by his discomfort.

Zuko breathes in deeply. "Want to what?"

"Want to fuck me," she says, as casually as if she were commenting on the weather and not incest.

"I don't..." Zuko does not continue because she is looking at him as if he is an animal doing people things. He grits his teeth.

"So how important is this dinner thing to you? You've asked every evening for the past, ugh, two years," Azula says, curling her toes. They brush against the soft crimson silk of her bed.

"Important," Zuko says, walking inside and shutting the door.

"I mean, I'm sure I'm the reason you can't get a girlfriend," Azula continues and Zuko sighs. The things he does for this girl.

Why? Helping Azula is not a very rewarding experience. It is at best tolerable and at worst unbearable. But he remembers his mother's words when she was a baby, and he knows he has a lot of protecting to make up for. Even if protecting Azula is protecting her from herself.

"Get the dress on the top of my third shelf," Azula says, clasping her hands over her concave abdomen. She seems entertained by this and Zuko fights the urge to just walk out.

He pulls open her creaking drawer, picks up the dress and holds it up. She nods.

She sits up slowly and crawls across the bed. He tries not to look as she stands up and takes off her pajamas. The ones she has not changed out of for a week.

"Okay, don't do that," Zuko says and Azula tilts her head to the side.

"Don't get dressed? Well, I can go to dinner like this if you'd like," she says and Zuko sighs. This is excruciating. "Why are you so afraid to look?"

"I'm not afraid to look at you," Zuko says and she waits. And waits. He shoves the dress into her hands.

"No. Put it on me. I asked you to help me get dressed," Azula says and Zuko does not know what to do. He is trying to erase the past. Part of him is certain that having sex with her made her lose her mind and he cannot do that again.

"This can't happen again. I made that clear," Zuko says and Azula chews on her lip. Hmph.

"You think that our fucking made me crazy, don't you?" Azula asks, smiling at the absurdity. "You do."

She laughs and Zuko grits his teeth.

Zuko replies, "It didn't?"

"Put my dress on me and find out," Azula purrs.

There is a slight pause as Zuko is thinking. He looks up and takes the dress from her.

She smirks in victory.

[X]

"Why did you ask me to stop that day?" Zuko asks one day. Azula squints at him for a moment before she realizes what he means. They do not even talk about sex when they are having it. Zuko's morality clouds him and Azula thinks it is sickening.

"To see if you would," Azula says softly. Zuko stares at her for a moment. "I didn't think you would."

"You didn't think I would? Of course I would. What kind of person wouldn't?" Zuko is utterly disgusted that Azula would think he was a rapist.

"Our father." She leaves the room as soon as she says it.

Zuko feels acid, but it is not panic or disgust or fear.

It is rage.

He confronts Ozai that day with a passion that makes his father clap sarcastically.

"And I thought you were such a coward, Zuko. But you're ruthless deep down, aren't you?"

Azula never finds out.

[X]

Day after day, Zuko watches his sister glide through the halls like a ghost. She is slowly changing, slowly melting and reforming over and over. She has given up on the violence, given up on the crown. But they do not meet eyes again.

Azula is in the courtyard, lying on the grass. Her chest barely moves with her breathing and Zuko realizes he is looking at her chest and feels that acidic panic again. It burns in his stomach and chest like a searing, ruthless fire.

He feels it every time he realizes he loves her in a way he should not.

"What do you want?" Azula asks sharply, not moving.

"Can I join you?"

"Only if you keep your mouth shut."

Zuko lies down beside her, staring up at the shreds of grey clouds in the indigo sky.

They lie there in silence for a moment.

Azula rolls onto her side and presses her lips against his.

"I'm not leaving again. And you aren't either," Zuko says as the kiss breaks. He feels wrong about it, sick about it, but that does not matter. "It's not happening."

"If you say so."

"Oh come on," Zuko snaps, not knowing why he expected anything else from her.

Azula shrugs and smirks.

He kisses her back.

end