Obviously the creators(Mike and Bryan) can't expect that everything is alright between Aang and Katara after that kiss in The Day of Black Sun, Part I:The Invasion. They haven't even talked about it so far. Here's a further development of their relationship.

Zuko shot a fireball at Aang, who was forced to disperse it. Aang gave a series of kicks, sending waves of fire at Zuko. It was part of their daily Firebending training.

I watched from a distance, by the pillars. My hand was on the cap of my water-skin, ready to attack, should Zuko ever try to hurt Aang. I really couldn't bring myself to trust Zuko, even if Aang trusts him. I haven't forgotten what happened in the Crystal Catacombs back in Ba Sing Se. Zuko betrayed us. I trusted him then, and Aang was nearly killed because of that. If it wasn't for the vial of water from the Spirit Oasis that Master Pakku gave me……

A hand suddenly landed on my shoulder. "Hey Sugar Queen, you're still watching over their training huh?"

I nearly jumped out of my skin. "Toph, for goodness sake, stop sneaking on me like that!" I hissed.

Toph merely grinned. "Don't you ever get tired of watching those two throwing fire at each other everyday?"

I gave a sigh. "It's just that I can't trust Zuko…"

Toph looked surprised. "Why? Hotman seems rather fine to me, even though he's not as funny as Sokka. What do you have against him?"

"It's a long story; I don't wish to talk about it." I changed the topic. "By the way, where's Sokka? I haven't seen him all morning."

For some reason, Toph smirked when I mentioned Sokka. "Oh, he's just inside trying to show off his swordplay, to Suki. And from what I heard, it doesn't seem to be going well."

That was so typical of my brother. He's been trying to show off to Suki ever since he came back from his "fishing trip". Just at that moment, Zuko had sent a huge wave of fire sweeping across the courtyard towards Aang. My hands instinctively went for my water-skin again. I held my breath, bracing myself to deflect it if the need arises. However, Aang had just dodged it, barely though, seeing that he wasn't allowed to use other forms of bending. The wave of fire passed a few feet from Aang, nearly burning him. I heaved a sigh of relief. But it wasn't over yet. Zuko had just sent another fiery kick, without hesitation, at Aang's head. Aang did a back-flip to avoid it. At the same time, he aimed a kick at Zuko's stomach. Zuko stepped to the side, grinning. My grip on my water-skin tightened. One wrong move…and I would not hesitate to kill him.

Toph laughed. "Hey Katara, relax. I could feel your heartbeat even if I were standing on sand. Hotman hasn't done anything bad to Twinkletoes so far. He's just teaching him."

I narrowed my eyes as Zuko gave another blast of fire at Aang. "I've trusted him once, and that mistake nearly cost Aang his life. Zuko's not getting another chance to hurt Aang again."

"Katara, how many times do I have to tell you that Zuko was not lying when he said he's changed? I could feel he was telling the truth!" Toph sounded exasperated.

"You could have been wrong." I frowned, even though she couldn't see.

"If you ask me, you're just being totally paranoid. Zuko's the only one Firebender who's willing to train Aang. And you're being downright obsessive, trying to take everything against the only one who's willing to train Twinkletoes. Come on, Sugar Queen. You love Aang, don't you?"

This question totally caught me off guard. My heart was hammering real fast. "No…of course not…I mean…how could I possibly……"

"I can tell you're lying." Toph said in an irritating sing-song voice as she folded her arms smugly.

"I'm not…" I could actually feel myself blushing as I turned away, glad that Toph was blind.

"Right, you're not lying," Toph rolled her eyes. "But I can feel your heart. It's beating faster than ever. Learn from Azula before trying to lie to me. I know you do love Aang."

I was about to retort when Zuko suddenly shouted. "Hey Toph, we need some targets here!"

"I'm on it, Hotman." Toph called back, walking over and starting to create moving pillars of rocks. They're done with the sparring, at last. Zuko drew his swords. I had a sharp intake of breath.

Zuko turned to Aang. "Firebending can also be channeled through any weapon. You could try using your staff with Firebending."

Aang nodded, picking up his staff. The duo started to destroy the rocks that Toph was bending. This shouldn't be too dangerous, since Zuko wasn't aiming at Aang anymore. Unknowingly, I started gazing at Aang. His lively ash-grey eyes caught my attention. Does he feel the way about me as I do him? I hope he does. After all, we had kissed twice, and I recall every moment vividly……

Our very first time, in the Cave of Two Lovers. Our only torch was about to run out. I placed my hand on his. A sudden feeling of exhilaration surged through me. I moved forwards, closer to him. He inched slowly towards me as well. The torch was getting dimmer by the second. He was getting too close. I wanted to pull away, yet my heart was yearning to get closer. He was just inches away now. Just a little closer. I closed my eyes. Then, I felt his lips on mine. It was a feeling I never had before. My heart was beating with excitement, wishing that this moment would never end. The crystals suddenly lit up. We broke apart. There was an awkward silence.

He spoke first. "They're made of some kind of crystals, they must only light up in the dark!"

That woke me up. I answered. "That's how the two lovers found each other. They just put out their lights and followed the crystals." Looking up at the crystals, I found the way out. "That must be the way out!" I turned to face him, giving him a brief hug.

He started to talk. "So, um…"

I cut him off. "Let's go." I wanted to hide my embarrassment……

The second time, was before the invasion, after we had passed the great gates of Azulon. It was rather awkward. We spoke at the same time.

"You go first," He told me.

I really did not know what to tell him. "We've been through so many things together…and I've seen you grow up so much. You're not that little goofy kid I found in the iceberg anymore. Well, I guess what I'm trying to say is, I'm really proud of you."

Silence again. Then he started talking. "Everything's going to be different after today isn't it?

"Yes, it is." I pushed my hair out of my eyes. I could not think of anything else to say.

"What if…what if I don't come back?" He suddenly asked.

I really could not imagine living without him. I had lost him once, and I did not want to lose him again. "Aang, don't say that. Of course you'll…"

Before I could complete my sentence, he suddenly stepped forth and put his lips to mine. I let out a muffled yell. This was all too…sudden. I closed my eyes, trying to recover myself. Then, before I knew it, he broke the kiss. I blinked and looked away. I knew I was blushing. His eyes had a determined look as he opened his new glider and took off. I turned around and watched him fly off. I was lost in my thoughts. What did he mean by that? I was confused, but I wished that moment could have lasted forever……

A sudden yell jolted me back to my sense. There was a flash of fire, and then I saw Aang lying on the floor, clutching his side. I nearly screamed myself hoarse. No, it can't have happened. I ran over and knelt beside him. "Aang! What happened? Are you alright?"

Aang groaned, closing his eyes. I stood and turned to face Zuko. "WHAT DID YOU DO?" I screamed in rage.

Zuko dropped his swords with a clatter. "Look Katara, it…it was an accident…I…I didn't mean to…"

"I've warned you…" I opened my water-skin and drew out the water, ready to unleash it all on Zuko. He hurt Aang. I've warned him before, one wrong move……

Aang suddenly grabbed my hand. "Katara, Zuko didn't mean to…" He moaned. I realized healing Aang was the priority. I gave Zuko a death look before kneeling down beside Aang. The hand on his wound was already stained with blood. Moving Aang's hand away from his wound, I bended the water onto my hand and placed it gently on his wound.

"Is Aang alright?" Zuko suddenly asked in a low voice.

I looked at him out of the corner of my eyes. "Get lost."

Toph tapped him on the shoulder and gestured towards the building. Both of them walked off, leaving me with Aang in the courtyard. I could feel Aang's breathing ease up a bit. He looked at me and smiled weakly.

"How are you feeling?" I asked, smiling back.

Aang suddenly leapt up. "I've always been fine with you around." He was staring at me with a weird expression in his eyes.

I felt rather uncomfortable. "Aang, don't stare at me like that."

"Why not?" He asked innocently.

I changed the topic. "I'm not done healing you yet…"

Aang took a step closer. "Katara, you know, there's an even better way for you to heal me." There was a sly smile on his face.

"What is it?" My heart was beating fast again.

He took another step closer. "This." He whispered, before pulling me into a kiss. No matter how surprised I felt, it was all forgotten soon. Within moments, I was lost in the kiss. I put my arms around his neck, and pulled myself closer to him. His arms wrapped around my waist. His bare chest was pressing closely to me. I closed my eyes, savoring every moment. There was a feeling of happiness that could not be traced. How I wished we could be together forever like this. After what seemed like an eternity, we broke apart, breathing hard.

A familiar question suddenly popped into my head. "What are we doing?"

Aang replied as if he had been expecting this question all the while. "What our hearts have been telling us to do for a long, long time." With that, he pulled me into another kiss. My heart soared. There was something oddly familiar about this. It was like a dream I once had. This feeling was like no other, it was like we were the only ones in the world; like we were in our very own world. I was running out of breath soon, but my heart desired nothing better than to just be with Aang, forever. Much as I would have liked it to last forever, we still had to breathe. I pulled myself away from Aang, panting heavily.

I had a question for Aang. "How long have you loved me?"

"Ever since I first set my eyes on you, when you freed me from the iceberg." There was a twinkle in his eyes.

My heart skipped a beat; we felt the same way for each other all along. Aang nipped playfully at my ear. "Baby, you're my forever girl." He whispered. I giggled, something that I usually did not do.