The chakra paper's reaction to Sakura's chakra confirmed Kakashi's long-held suspicion that her primary nature was fire. After all, she'd learned the Great Fireball Jutsu on her very first try the moment Sasuke had finished teaching it to her.
"The most common affinity among the citizens of the Land of Fire is fire," Kakashi-sensei explained to Naruto. "Moreover, Sakura belongs to the Uchiha clan, famed for their chakra's natural fiery quality."
Naruto nodded. That made sense, he had seen Sakura and Sasuke spit out fireballs more times than he could care to count.
"Why didn't you give us this test three years ago, when we were just starting out?" Sakura complained on behalf of Naruto. "Wouldn't it have saved us a great deal of trouble?"
Naturally, the answer to that question was that Kakashi simply couldn't have been bothered to administer the chakra paper test back then. Of his three disciples, the only one he had tested was Sasuke, his beloved— just before whisking him away to prepare for the Chūnin exams' finale.
"Chakra paper is costly," Kakashi-sensei said with a shrug. "Turnover rates for shinobi fresh out of the academy are quite high— and also I wasn't sure it'd be worth spending money on a bunch of egotistical brats who might drop dead the very next day."
Sakura rolled her eyes. She knew he was just being a tsundere again.
"You're kidding, right, Kakashi-sensei?" gulped Naruto. "You don't really mean that, ya know!?"
"Who knows?" said Kakashi lightly, smiling behind his mask. "In any case, back to the point, your affinity is wind, Naruto… which is rather uncommon in the Land of Fire. It's far more prevalent in the Land of Wind, and its offensive power in close to mid-range is quite strong— wind Ninjutsu are quite good at tearing, cutting and severing."
A goofy grin appeared on Naruto's face again. Who didn't like feeling special, after all?
"That's not to say it's only good for cutting," Sakura added quickly. "I mostly use Wind Style as a replacement for Water Style. I don't like seeing blood, so I mostly use techniques that throw concussive shockwaves to knock out my enemies."
Kakashi gave a pointed cough to steer the conversation back on track.
"Mastering nature transformation isn't as easy as mastering shape transformation," said Yamato, jumping into the conversation. "It usually takes months to learn to use your main chakra nature, and it can even take up to a few years in certain cases, depending on your affinity."
Naruto frowned— something wasn't quite right.
"Then what about Sakura?" he asked pointedly. "They only taught us the three basic techniques at the academy, but she was pulling off all sorts of crazy Ninjutsu within a few months, you know?"
She wasn't from a ninja family— he knew that for a fact— so it wasn't as if she'd been trained in elemental Ninjutsu beforehand. And if it really took years to master even one nature, how had she managed to learn so many, so quickly?
"Isn't it obvious?" said Sakura smugly, folding her arms. "That's because I'm a certified genius."
It felt weird, being able to cross her arms in front of her so easily, and then not having a huge weight resting on her forearms…
Naruto looked thoughtful again.
"Just wondering," he said slowly, "which nature does your Wood Style fall under, Captain Yamato?"
Kakashi leaned over and whispered something into Yamato's ear. A shit-eating grin appeared on Yamato's previously uninterested face, and he started weaving hand signs.
"Earth Style: Rampart of Flowing Soil Jutsu!" + "Water Style: Waterfall Basin Jutsu!"
Naruto backed away swiftly as the ground began to rumble, cracking open beneath him. A great wall of earth surged upwards, lifting Yamato high into the air. Then, an underground source snaked up and burst through the top of the earthen rampart, cascading down in a waterfall that pooled at the feet of Naruto, Sakura, and Kakashi.
Sakura clapped politely, recording every single hand sign with her Sharingan, while Naruto oohed and aahed at the extraordinary display.
"I have both earth and water chakra natures, Naruto," Yamato shouted down from his perch.
"Just because you weren't born with the nature you wanted doesn't mean you can't train yourself to use it," Kakashi explained. "By the time most shinobi reach Jōnin rank, they've usually mastered at least one additional nature alongside their primary. Like Sakura, I can use all five— fire, wind, lightning, earth, and water."
A look of confusion appeared on Naruto's face. Then, what about wood?
"Remember Haku's Ice Style?" said Sakura preemptively. "All chakra natures that aren't one of the basic five are Kekkei Genkai, the simultaneous activation of two or more of the five basic natures— which in Haku's case, is water and wind."
"Exactly," completed Kakashi. "That's why I couldn't copy his techniques with my Sharingan."
"Just like the Sharingan, then…" said Naruto, chewing his lip in thought. "I dunno… doesn't seem like they're quite the same thing, you know…"
For a shinobi who had mastered more than one chakra nature, using them one at a time was simple enough. But only those born with affinities strong enough to qualify as primary could awaken— or inherit— a Kekkei Genkai. And only Kekkei Genkai users could activate multiple natures at once, blending elements to forge an entirely new one.
For instance, Kakashi and Sasuke couldn't breathe fire and simultaneously cloak their hands in lightning, despite their strong affinities for both elements.
"Just watch!" called out Yamato. Sakura watched attentively as he weaved a few hand signs before clasping his hands together. "Earth in my right hand, and water in my left."
A row of trees began to sprout along the middle of the earthen rampart, growing rapidly upwards in a neat formation as they sought sunlight. Once he'd seen enough, Naruto turned to Kakashi, ready with another question— this time about Sakura's Medical Ninjutsu, her Genjutsu, and the Ino-Shika-Chō's Hiden techniques, which didn't seem to fit into the five-nature system at all.
Kakashi sighed.
It was a good thing that Naruto was finally beginning to get interested in learning, but honestly, he just couldn't be bothered explaining… and even if he did, Naruto's pea-sized brain wouldn't understand anything about Yin and Yang Style.
"Hm? What are you doing, Sakura?" said Kakashi, sensing her kneading chakra as she slowly replicated Yamato's hand signs. "I just said there's no point, the Sharingan can't copy bloodline lim…!???"
A green leaf poked through the soil. Then, slowly but steadily, the green shoot rose higher, unfurling into a small sapling. It kept growing taller and fuller, sprouting branches and clusters of fresh leaves, until it overtook Sakura's height, then Kakashi's. Its trunk thickened, stretching skywards, until a majestic tree stood before them, towering over Yamato's earthen rampart.
For the first time in his life, Kakashi was genuinely speechless. Yamato's face fell— could he really keep calling himself Tenzō of the Wood Style if he no longer was the sole user!?
"You're full of it, Kakashi-sensei," said Naruto reproachfully. "I bet you're just too lazy to try!"