Author's Notes: I don't own Avatar: The Last Airbender.
In the heat of the moment there was nothing else he could do. If there were other choices (and sometimes he wished there were), he would consider those choices first. It wasn't a secret how much he cared about Katara, and he even admitted it to Guru Pathik when he was helping him control the Avatar State via chakra control. The only way he could save her (the only way he could save her world) was to let go of his feelings for her. There wasn't another way, and it pained him to even think about letting her go in such a manner, but it had to be done.
He looked down, and closed his eyes as if he were ashamed of himself for even doing so. "I'm sorry Katara..." was all he could muster to say before sheltering himself with the crystals through earth bending.
He sat down in his meditative position, and began to think of all his earthly attachments. Katara's figure danced across his mind in a vision of violet that seemed to blur within every second of his meditation. Every image and memory he had of her began to fade away; the memory of their first kiss in the dark was the last vision to go. It slowly faded, and he felt it go. It was torturing him because he started to feel how he felt that day. He remembered how fast his heart was beating, and how he felt her warm breath against his cheeks until they both leaned in. He remembered how quick he was to respond when he felt her lips brush against his suddenly, and how he caught her own lips with his to give her a small, but gentle peck.
Before he could hold on to the memory for a bit longer, it blurred away into space. He found himself floating and walking down the purple path that led to his astral self. He entered the ball of energy formed by it, and felt himself become one with the Avatar spirit.
With a beam of light he rose, and with a new mastery of everything around him he was ready to take on all who dared challenge him. Suddenly, he felt a scorching heat that started from the sole of his shoe, and then ran upwards to the top of his spinal cord.
Everything went dark then, and his eyes closed slowly before focusing on Katara. He saw her cry, and then faded into nothingness.
It wasn't until he felt a cool, but warm touch that he awoke from his unconsciousness. He opens his eyes, and sees a pool of blue looking at him with surprise. (He feels it now more than ever, and knows that he had fallen in love with her once again) She smiles, and a few tears spill from her eyes before she holds him a gentle, but assuring embrace.
He wishes to hold her, but he feels numb so he can't. Before she lets him go, she gives him a soft peck on his forehead where his arrow tattoo glowed not too long ago. He smiles, and she smiles when she sees him do so.
"The Earth Kingdom has fallen..." The king says to them, and Aang slowly fades to nothingness once more to rest, and thinks of himself fallen as well, but if Katara could catch him when he did, then they will be able to restore the Earth Kingdom like she had done for him.
All they have to do now is hope for the best, and wait.