Much like the other buildings in Sunagakure, the infirmary was a hive of dimly lit rooms and connecting hallways, and as such, it was only by chance that Kakashi noticed Mayu being carried past on a stretcher.
Once he'd affirmed that Naruto's condition had stabilized, he had worried over her battle against Fū – and as soon as he saw the blue hair clips attached to a mop of sandy hair, Kakashi jumped to his feet and stopped the medic nin in order to check on her.
But even without the medic assuring him that she would be alright, with just a cursory look over, he could tell that his fears had been groundless. Mayu was bleeding from what looked like multiple tiny perforations on her arms, but that appeared to be the extent of her injuries. She was breathing steadily, with no irregularities in her pulse; it appeared she was merely unconscious.
Relaxing, Kakashi nodded and stepped back, allowing the medic to direct her stretcher to another room.
Just as he'd walked back through the doorway, he saw Naruto's eyes snap open. Leaving the stunned boy to stare up at the clay ceiling from his prone position in bed, Kakashi locked the door behind him and checked the room once more. They were the only occupants in the room, and the medic who had been attending to Naruto had long since left.
But of course, that didn't mean anything in a hidden village like Sunagakure. He would have preferred to take Naruto to a more secure location, but to do so now would attract unwanted attention. Passing his hand over his face, Kakashi lifted his hitai-ate to reveal his sharingan. Glancing around, he was rewarded with a small chakra presence perched on top of the rim of the nearest window.
"Kakashi-sensei?" Naruto asked in a taut voice. "What happened? ...I passed out again, didn't I?"
Without responding, Kakashi leisurely ambled over to the window. Pretending to look outside at the view of the drab, open field of sand in deep contemplation, he saw that the source of the chakra was a harmless beetle on the outside.
The inside on the other hand was a whole different story. From what he could tell by its thin string of light chakra that jutted out from its posterior and led out of the room, it was a modified puppet, possibly with the added capability of recording conversations. Ingenious, what some of their jutsu could accomplish. However...
With an idle flick of his fingers, Kakashi squashed the insect against the wall, before turning back to face the genin. As soon as he met the boy's blue eyes, he internally winced; the pressure of the daunting task that loomed before him weighed down on him all at once like a massive boulder. Kakashi pinched the bridge of his nose, gathering his thoughts together. Nevertheless, it has to be done... – and with that thought in mind, he let out another exhale.
"Naruto," he began at last, "before anything, I would like to apologize."
The genin looked taken aback. "Apologize? What for, sensei?"
"In my defense..." Kakashi paused. "No, I have no defense. The truth of the matter is that everyone, including me, has been lying to you for your entire life. I could have done something about it, but I never did. I'm sorry."
"...I see." To Kakashi's surprise, Naruto's gaze sharpened. "And I suppose these lies have something to do with why I am passing out. Are you going to tell me what these lies are?"
"Yes," he replied, and was gratified to see a look of surprise flash across the genin's face. "I'm going to tell you everything that I know, consequences be damned. While it isn't much, it's the very least you deserve..." Kakashi trailed off, as a sudden thought struck him. "I'm assuming that you want to hear the truth?"
"Yes, sensei," said Naruto immediately. "Right now, please."
Kakashi nodded. "Very well. But there's one thing I'm going to ask of you. And that's to hear me out in its entirety. Some news might – will – be shocking to you, but I want you to stay here on your bed. In return, I promise you that I will tell you the entire truth as I know it."
"Yes, sensei," Naruto said, his tone now touched by a slight flavor of impatience.
"Alright then." Kakashi took a deep breath. Might as well get it over with from the get-go. "You are a jinchūriki." At these words, he noted that Naruto's face remained unchanged, but could sense his body tensing up. "That means that you are the host of a tailed-beast. In your case, during its invasion of Konoha, the Nine-tails – Kyūbi – was sealed within you when you were a newborn baby."
"The Kyūbi wasn't destroyed?" Naruto asked, raising a fist to clear his throat. His face was otherwise, curiously devoid of emotion. "I thought the Fourth Hokage defeated it."
"Tailed-beasts aren't so simply defeated, Naruto," said Kakashi. "They're mammoth living forms of chakra – the best we can do is seal them away. And most villages take advantage of this by sealing them inside another living vessel – a human."
"Was it a complete seal – is that even possible? How come it's never gotten out?" Naruto frowned. "It has, hasn't it?"
Kakashi nodded. "Correct. However, from what I know, there has been only one incident so far in which the Kyūbi managed to temporarily escape its seal. It happened when you were six – or actually, the day before your sixth birthday. Some foreign ninja somehow managed to get intel on you and infiltrated Konoha. In the incident, you lost control and managed to kill them all."
"But I don't remember – "
"There are gaps in your memory, Naruto. Ever since that day, for five years now, there has been a seal on some of your memories." It was curious and yet disheartening to observe the careful look of calm beginning to fall apart on the genin's face, like cracks in a sheet of ice that had frozen over a raging river. Before he could be swept away in its current, Kakashi hurriedly pressed on.
"It is a type of forbidden fūinjutsu called the Genkōkin Fūin (Taboo Seal). It was invented by the Fourth Hokage, and was popularly used during the Third Shinobi World War – it works by making a word or idea 'taboo' in someone's mind.
Any time they begin thinking about it, the seal immediately sucks the memory away. People whose mental resilience is strong enough tend to unconsciously fight this, and suffer tremendous headaches as a result. That's the reason why you've been falling unconscious. Your mind has been fighting with the seal, trying to hold on to your memories. As a temporary measure, I've put a block on the seal for now, which is why, as I tell you this, you aren't falling unconscious."
Naruto's hands fell by his side. A long, terse silence entangled itself around them. Looking at the mixture of feelings playing out across his student's normally stoic face, Kakashi had to hold himself back from sighing. Ninja lived harsh, often unjust lives, and it was something that he had come to accept a long time ago as a child himself. But something about the way Naruto's face looked like just now brought back memories of those grey, rain-drenched days he'd spent in the reflection of the cold memorial stone.
"Why me?" Naruto finally let out.
"The Fourth Hokage chose you," Kakashi replied.
"Why?" Naruto repeated, shaking his head. Kakashi hesitated. "Please, sensei."
"Because you were his son," he said quietly.
"What?" Naruto blurted out, looking at Kakashi in naked disbelief. "But that's..."
"Your father was Namikaze Minato, the Fourth Hokage," Kakashi pressed on. "He was my teacher, and a legendary shinobi renowned as Konoha's Yellow Flash. He died a hero, saving the village by sealing the Kyūbi inside his own child – you."
Naruto didn't respond, and as Kakashi watched the genin's eyes slowly turn dull, the weight on his back seemed to grow heavier and heavier. He wondered if he had made a mistake – not about putting a stop to the memory seal, but about the timing of it all.
Perhaps he should have waited for a more optimal time before revealing the truth to the boy? But with the memory seal quarantined off, Naruto would have woken up immediately knowing that something was off, and it would have been damaging to their tentative trust if Kakashi had continued denying him the truth of everything.
"I can't say that I understand completely why Minato-sensei made his decision," said Kakashi, choosing his next words with care.
"And I know you were in a lot of pain growing up because of that...We were all forbidden to tell you anything, because we were told it would be safer for you to remain ignorant of your circumstances. But, I want you to know that your father must have had a very good reason to do so, because that's just the type of ninja he was. His last wish was for you to be seen as a hero."