Aang looked down at the candle in Katara's hand. Its light was diminishing quickly, exactly the opposite action his heart was taking. It was beating hard against his chest, but not out of fear of darkness or being lost forever in the seemingly endless caves. He could feel a kind of nervous excitement fueled by the anticipation of what was about to happen.
The flame flickered dangerously, causing the boy to emit a soft gasp. Katara was now ever closer to him than she had ever been before, and here they were, in the Cave of Two Lovers, about to do something they'd never done before.
There was a force of gravity between the two of them, it seemed, as their faces moved closer to each other's. Aang could see Katara's eyes begin to close slowly as the candle gave its last flare of light, leaving the two of them engulfed in the darkness.
Their lips touched, and Aang was frozen in shock and disbelief. She was kissing him, and she wasn't pushing him away; in fact, he felt her hand upon his cheek as another sign of affection. The two of them stood silently with each other, sharing the kiss in a silent mutual intimacy. It was a moment unlike any other that Aang had experienced in his past.
But then, just as soon as it had begun, their close contact came to an end with a surprising observation: the ceiling of the cave was now glowing with beautiful azure crystals. The two sweethearts broke apart from each other to gaze upwards, to what might have been glimpses of heaven through a clear night sky.
Aang looked at Katara, whose soft features were quietly illuminated by the sparkling blue light. Although he couldn't quite tell whether the shadows were fooling him, Aang suspected he saw a hint of a blush on her cheeks.
The two looked at each other for a moment, with muted disappointment that their moment of union was now a fragment of the past. Because they were unsure of what to say after that, the couple began to follow the trail in silence.
Aang couldn't bring himself to say anything more or to speak of how much his emotions told him that the kiss felt perfect, and that he'd like to do it again... but he couldn't risk losing a friend like Katara.
All that he had now was the afterglow of his now most precious memory.