After checking Karin's abilities, Yorin felt it would be better for her to learn from his "master's wife" rather than from him—meaning Tsunade.
Karin had talent in medical ninjutsu, and her chakra reserves were pretty decent. Also, even though she'd never had systematic taijutsu training, the Uzumaki clan's strong physical constitution was often shown in the original story.
With all that combined, Yorin thought there was no one more suitable to train her than Tsunade.
Tsunade would teach her, and once Karin went home, her godmother Kushina could teach her too. Having Konoha's two biggest "mama-tigers" teaching one person—what kind of blessing was that?
But guess what? When Yorin offered Karin that "best possible" arrangement, she didn't like it.
"Huh? But Teacher… aren't you the one who's going to teach me?" she asked.
Yorin explained his reasoning and laid out the whole analysis, but she still wasn't happy.
"Even so, I still want to stay with you, Teacher. It's fine even if I don't learn anything. You wouldn't let me lose out anyway, right?"
Yorin: "…"
He got the distinct feeling she had ulterior motives.
He really wanted to roll his eyes.
Just look at Sakura and Kakashi in canon.
Kakashi was way too biased—though Sakura not pushing herself was part of it too.
Still, Sakura followed Kakashi for ages and he taught her basically nothing. It was bizarre.
Yorin believed he'd treated Karin far better than Kakashi treated Sakura—he'd done his duty as a teacher.
And yet she still wouldn't accept it.
Yorin: "Is this… because I'm too charming?"
Being handsome isn't all upside.
Feeling helpless, he carefully asked his girlfriends for a reality check. He got several eye-rolls, plus a rhetorical, "Yeah—what else would it be?"
That left Yorin forced to admit, yes, it was his charm.
But it wasn't his fault. In the end, he decided to let Tsunade handle Karin.
Time would fix it.
Yeah. Definitely.
…
That's the downside of being handsome—but there are upsides too.
Like the next part of the plan: Yorin felt extremely confident it would go smoothly.
Black Zetsu: "Are we going to capture tailed beasts?"
He asked eagerly, only to receive a faintly pitying look from Yorin.
That look made Zetsu uneasy, but he still forced himself to ask again:
"...We're going to capture tailed beasts, right?"
So.
Near Uzushio Village, in a hidden valley no one knew about—
Yorin: "The tailed beasts aren't 'not being captured.' They're being captured slowly, steadily, and according to plan."
"And before I start capturing them… I still need to do something first…"
In other words: free Uchiha Hikari.
He'd talked about freeing Hikari again and again, but it had always been talk.
This time wasn't just talk.
…
Some readers might ask:
Can "top-build" Uchiha Hikari—at her peak—beat Kaguya?
Obviously not.
But that was never the point.
Yorin wasn't freeing her to have her solo Kaguya.
He was freeing her because he wanted to.
Freeing her would make him feel good.
And while feeling good, he'd also gain +2 to his "Essence" stat—by "fighting Hikari properly" and earning the achievement "Overpowering an Uchiha Prodigy."
Also, he'd indirectly asked the Second Hokage about it before. Tobirama looked utterly baffled, like: "Huh? You can do it like that?"
So the "system" probably wasn't Tobirama's work. Which made sense—if he could do that, he wouldn't have gotten taken out by small fries like the Gold and Silver Brothers.
…
So the "Rescue Hikari" operation began.
"This seal… yeah, it's the Uzumaki clan's work. But it's fine—I prepared for it."
Back in their prime, the Uzumaki were seriously something. Even a "genius" like Yorin needed a lot of time to sort through and dismantle the layers.
As the seals peeled away one by one, he finally saw what he'd been looking for—
A coffin, sealed within the formation.
Yorin jumped down into the pit, lifted the lid, and there she was:
Uchiha Hikari's face—shockingly adorable.
Time hadn't taken away her beauty at all. She lay there like she was simply asleep.
A sleeping beauty.
Too cute. Ridiculously cute.
"Ah… ah… if this were a fairy tale, am I supposed to kiss her?" Yorin couldn't help thinking.
If it were one of his other women, they'd scream that he was being shameless.
But Hikari… maybe she wouldn't?
Meaning…
…No. Better not.
Because Yorin had already noticed her eyelids twitch.
Hikari was about to wake up.
So instead, he decided to greet his "great-great-grand-elder" with a gentler smile.
If you take the sleeping beauty trope literally, the classic variation is: she opens her eyes, blushes, thanks the hero, and maybe even asks to repay him with her life.
Then the hero says: "Grandma… you've been asleep for a thousand years."
Lifespan jokes and taboo age gaps are the cruelest—and funniest—things in the world.
Luckily, Yorin didn't care about that stuff. If he did, he wouldn't be "that close" with Tsunade either.
"…Where am I? What… happened to me…?"
After a brief haze, the sleeping beauty finally opened her eyes—and met Yorin's smile.
For a moment, a warm feeling filled her chest, as if she'd been held by something gentle.
Given how she'd been trained and what she knew, she should've been wary, hostile—she could even have attacked right away.
But she didn't. She just looked at that smile, quietly.
They held that pose for a long time, until Hikari's mind cleared and she regained her calm.
"Uchiha…?" she asked cautiously, looking at him.
Back when she was alive, the Uchiha had treated her like a weapon—used her like a tool. She had no fond feelings toward the clan.
Her first impression of Yorin was good, but once she saw his unmistakably "Uchiha" features, her guard rose sharply.
"You may not understand the current situation yet. I can explain," Yorin said gently, and he gave her a broad outline—from the Warring States era, to the hidden villages, to the present.
"So you're the current clan head of the Uchiha?" she asked.
"Yes."
"Then… why did you release me?"
Even as she asked, she already had an answer in her heart:
Because I'm powerful.
Because he wants to use me as a weapon.
Because he wants my strength to help conquer the world.
But Yorin's reply made her blink in confusion.
"I don't need that," he said. "I think you've misunderstood."
"I don't need you as my fighting force—or the Uchiha's. For the Uchiha and even the ninja world today, our combat power is already enough."
"Then you…" Hikari grew even more puzzled.
She'd been the "ultimate combat unit" for so long.
If she wasn't meant to be that… what was she meant to be?
"A partner."
"…A partner?"
"Yes. A partner."
"I don't know what the Uchiha were like in your era," Yorin continued, "but under me, the Uchiha are a clan that values comrades."
"When I found records that an Uchiha still existed out there, I decided I would free you."
"As for freeing you and then 'using your power' for something—I never planned that."
"If you want to leave on your own, I won't stop you. I just suggest you return to our clan grounds first, rest, learn how the world works now, and prepare supplies."
"…And if I refuse?" Hikari asked, still wary.
"That's fine too," Yorin said. "I'll give you books and travel money. I'll also tell you how to contact the Uchiha. If you run into trouble, message me—I'll help."
"…That's all?"
"That's all."
Hikari watched him carefully. Yorin met her gaze steadily, without flinching.
After a long moment, she finally nodded. "I can go and see. But don't expect me to be grateful."
"I wouldn't," Yorin smiled. "Then… will you take my hand?"
Still uneasy, but no longer resisting, Uchiha Hikari reached out.
The moment their hands met, she felt warmth—and then the world spun.
In an instant, they vanished from Hikari's sealed prison…
…and reappeared in Konoha, in Uchiha territory.