They had been fighting, the two of them. Itachi wasn't sure why Kakashi insisted on fighting him so fiercely. Itachi's skills were obviously superior, but they were never enough to make the other man back down. Was he that desperate to protect Konoha? So desperate that he would always set himself up against Itachi, knowing that it would only end in pain? Itachi had better things to do than squander chakra, but when he tried to flee, the Copy Ninja followed him. Followed him into a cave, where Itachi was forced to resume the battle.
How did the rockfall start? Perhaps it happened when Kakashi was slammed into the cave wall. Or maybe when Itachi's shuriken missed their desired target, and hit a loose rock. Itachi didn't know how it happened. All he knew was that he and Kakashi were suddenly engulfed in an raging downfall of rocks. Not just rocks: ENORMOUS rocks, big enough to crush someone...Kill someone.
Self preservation kicked in. Itachi dashed to the exit, not caring that his enemy was right beside him. Their once different goals were suddenly common: Get out alive. Right now.
But that was proving to be extremely difficult. The entire place was caving in. Itachi found it ironic that his life could be taken in something as simple as a cave-in. How pathetic. All the ninja he had defeated, all the jutsus he had mastered, all the skills he had learned- Meaningless. And as the largest rock yet flew towards him, he froze. All he could do was watch, as certain death plunged towards him. Time seemed to slow down, but his mind raced. 'This is it? THIS is how I go? Stupid...How could I be...So careless...?'
His eyes were shut. All he could hear was his blood rushing and- A shout? A pair of arms wrapped themselves around Itachi. For a split second, it was just him and those warm arms. Then he was violently thrust away, slamming into the ground, tumbling...Then stopping. It was too quiet. Itachi forced his eyes open. The avalanche of rock had finally ceased. He was alive. He glanced to his right- The opening of the damned cave. And to his left- Kakashi Hatake. Or...Part of him. His entire right half was crushed. Crushed underneath the same rock that, only moments before, had been Itachi's imminent death. Itachi's scrambled thoughts came to realize the obvious. Kakashi had thrown him out of the way. Kakashi was the one under the rock, drenched in blood, not Itachi. Kakashi had...DIED for him.
That was when his head started to ache and his confusion began. Why? That was the only thought Itachi could focus on. He and Kakashi weren't friends, they were enemies. Even before Itachi had left Konoha, they hadn't been close. They had barely spoken to each other. They had both been in ANBU, but that meaningless bond wasn't worth dying for. Especially since Itachi was now classified as an S-Rank criminal. A threat to Konoha, the very place that Kakashi had vowed to fight for. Nothing made sense, and Itachi just sat at the cave's opening, staring at the broken Copy Ninja, and racking his brain.
Then it dawned on him. Kakashi had mistaken him for someone else. Satisfied with his simple conclusion, Itachi stood up, briefly checked himself for injuries, then walked away. He felt no guilt in leaving Kakashi's body behind, even if he had just saved his life. The man was dead, and giving him a proper burial wouldn't make him any less dead. It would just waste time. Besides, what did the Uchiha owe him? It wasn't really Itachi he had been trying to save. Itachi knew it. During the utter chaos of the rockfall, amidst the fright and confusion, right before he grabbed Itachi- Kakashi cried out "Obito".