Kakashi looked at Seiryu. In many ways, they were similar—both had Sharingan, specialized in Lightning Release, and were skilled swordsmen.
So Seiryu probably had ways to help him improve.
"You've used my clansmen's Sharingan well, but you're too fixated on typical Uchiha combat methods," Seiryu said. "Using Sharingan to copy jutsu is handy, but your chakra reserves can't handle the cost. Even real Uchiha only use a few well-practiced jutsu against strong foes."
"So, what you should improve is chakra control." With that, Seiryu formed a hand seal.
Thick lightning appeared, forming into a human shape. As details sharpened, Kakashi saw that the lightning man looked exactly like him—even its expressions matched his own.
"This…" Kakashi was stunned, raising his forehead protector to gaze with Sharingan.
What Seiryu had done wasn't a Lightning Clone or even a jutsu—just pure, precise control over chakra's form and nature. Even Tsunade, famed for her control, couldn't compare.
Seiryu snapped his fingers—the lightning man vanished. "If you can do this, you can achieve this much with minimal chakra."
Seiryu pulled out a kunai and infused it with Lightning Release chakra to create an electromagnetic field.
Before Kakashi's disbelieving eyes, the kunai floated and began spinning rapidly. Seiryu pointed, then clenched his fist.
In an instant, the spinning kunai shot out at a speed even Kakashi's Sharingan could barely follow, smashing a one-meter-wide boulder into pieces.
Kakashi was floored. While a jonin could do similar damage with jutsu, the kunai's speed approached Mach 3—faster than most could dodge. Most importantly, the chakra Seiryu used was less than a basic Clone Jutsu.
"How did you do that?" Kakashi asked.
"Kakashi, have you ever explored the currents produced by Lightning Release's nature transformation?" Seiryu grinned. "If you master control, you can make a strong magnetic field and accelerate metal objects. I call this move the 'Railgun.'"
"If you learn it, your chakra shortage won't matter."
He tossed Kakashi a scroll. "Practice what's inside. Besides me, only you can learn this. Without Sharingan's dynamic vision, even aiming is hard. My other clanmates aren't talented in Lightning Release."
"This is too precious," Kakashi said.
"Then trade me your Chidori. I'll teach it to Sasuke. My own jutsu aren't suitable for beginners." Seiryu replied.
Kakashi smiled wryly. His hard-won Chidori was just a basic skill for Seiryu? But thinking it over, aside from White Fang's blade, Chidori was the only thing worthy of Seiryu's technique.
"I'll bring the Chidori scroll before I leave," Kakashi promised.
"Take this too, for the Mist." Seiryu handed over the Kuburi blade.
"Is that necessary?" Kakashi asked, puzzled. "I haven't practiced swordsmanship in ages."
"It's not for you to use," Seiryu smiled. "For Mist missing-nin, just seeing it is more effective than any jutsu."
"Alright, understood." Kakashi accepted the blade, trusting Seiryu's judgment.
…
The next day, Kakashi received his mission. As Seiryu predicted, he and Minato's old team—including Genma—were grouped together to assist in clearing Mist missing-nin on the southeastern border.
That afternoon, Kakashi picked up Naruto and headed to the Uchiha compound.
"Big Brother Kakashi, where are we going?" Naruto asked, realizing this wasn't the way home.
"I've got a long mission, so I'm asking Lady Mikoto to look after you," Kakashi said.
"Eh?" Naruto was surprised. "I can take care of myself!"
"Take care of yourself as in eating ramen every day?" Kakashi shot him a look.
"Uh…" Naruto stuck out his tongue, caught.
"So, I'm staying with Sasuke?" Naruto asked.
"Don't want to?" Kakashi replied.
"No, it's fine." Naruto shook his head. Despite fighting Sasuke daily, he valued him as a friend and was happy to live together.
"But come back soon, okay?" Naruto looked up at Kakashi.
Kakashi ruffled his hair. "I will—I'll come back as soon as I can."
…
At the Uchiha compound, Mikoto—dressed as a housewife—answered the door, surprised to see Kakashi and Naruto.
"Kakashi? Naruto? What brings you here?"
"Hello, Aunt Mikoto!" Naruto greeted.
"Lady Mikoto, I'm going on a long mission. Could you look after Naruto for a while?" Kakashi asked.
Mikoto nodded but glanced at Naruto. "Looking after him is fine, but…"
She trailed off, but Kakashi understood. As friends of Naruto's parents, caring for him briefly was acceptable, but having the jinchūriki live in the Uchiha compound would make the village elders uneasy.
"It's fine," Kakashi said. "With you looking after him, no one will object."
"Alright," Mikoto agreed. "Want to stay for dinner?"
"No need, I need to pack." Kakashi declined, then told Naruto, "Don't trouble Lady Mikoto while you're here, alright?"
"I know." Naruto nodded.
At that moment, Sasuke peeked from behind Mikoto.
"Naruto? Are you staying with us?"
"Yes," Mikoto patted Sasuke's head, smiling. "Be good to each other, okay? Sasuke, show Naruto in."
"Okay!" Sasuke grinned and led Naruto inside.
"Sorry for the trouble, Lady Mikoto," Kakashi bowed.
"Don't mention it," Mikoto replied softly, watching Naruto go. "After all, he's Kushina's son."
…
After leaving the Uchiha compound, Kakashi returned home and found Jiraiya waiting.
"Lord Jiraiya?" Kakashi feigned ignorance. "Is something wrong?"
"Is Naruto not home yet?" Jiraiya asked.
"I'm going to the border for a while, so I asked someone else to look after him."
"So you sent him to the Uchiha?" Jiraiya said sternly.
"Is there a problem?" Kakashi replied. "If Kushina-sensei were alive, she'd make the same choice."
"Kakashi, Naruto is the jinchūriki! You shouldn't send him to the Uchiha." Jiraiya insisted.
Kakashi's face suddenly changed: "Jinchūriki! Of course I know that! But he's also a seven-year-old kid! My teacher's and your student's only son! Are you here for him, or for the jinchūriki?"
Jiraiya flushed, but still argued, "Have you considered what would happen if the Uchiha controlled the Nine-Tails?"
"Lord Jiraiya, with your position, you shouldn't say such things," Kakashi warned coldly.
Jiraiya realized his words were too sensitive and checked that they were alone before sighing, "Kakashi, I don't mean that, just being careful."
"Lord Jiraiya, the Uchiha's pride wouldn't allow them to use a child like that," Kakashi said.
Jiraiya was silent. He wanted to say the Uchiha wouldn't stoop so low, but he couldn't say so with confidence.
As advisor, he'd read all the files left by the previous elders. The rumors about Naruto and the Nine-Tails were orchestrated by Danzo, not the police force—they never took part in spreading those rumors.
So, faced with Kakashi's words, Jiraiya could only remain silent.
"Lord Jiraiya, please go. If you want to see Naruto, visit the Uchiha. I'm sure Lord Fugaku and Ldy Mikoto won't refuse." Kakashi said, then entered his house and closed the door.
Jiraiya looked at the closed gate of the Hatake compound, sighed, and headed for the Hokage office.
He walked in, dejected. Hiruzen saw him and sighed as well, guessing Jiraiya had hit a wall with Kakashi.
"Kakashi still insists on letting the Uchiha care for Naruto?" Hiruzen asked.
"Yes," Jiraiya nodded. "Old man, you guys went too far before. Now Kakashi trusts the Uchiha more than us."
Hiruzen lit his pipe. "Is it about the rumors regarding Naruto? Danzo acted behind my back. By the time I realized, it was too late. If I tried to explain, it would only deepen the villagers' suspicions."
Jiraiya looked at his teacher for a long while, then shook his head. "Forget it. The Uchiha wouldn't go so far as to harm a child. Old man, have you picked a new ANBU Captain now that Kakashi's left?"