Kaien had a very good reason to replace both of his natural eyes. As incredible as the Kamui Sharingan was, relying solely on it meant walking around with a massive target on his back. The moment he transplanted that eye, he knew Obito Uchiha would stop at nothing to tear it back out of its socket. Worse still was Zetsu... a creeping spy who could be lurking anywhere and would be impossible detect as a yin-yang being unless ofcourse you are Hashirama which he is not.
That was where the Byakugan came in. To survive the future, the white eye was just as vital as the Sharingan. It would be his ultimate radar, a constant alert mechanism against Obito who is specialized in surprise attacks. Moving forward, he'd need to keep his guard up every second of every day, always anticipating Obito stepping out behind him.
Well, now that is done... he need to take care of other things.
"To keep Obito from pulling any unscripted tricks like Izanagi, I need to fast-track the 'Free Bird' seal onto the rest of the Uchiha," Kaien thought, running through his mental checklist. "Fugaku and Mikoto already have it, which should make persuading the rest of the clan a lot smoother. Once everyone is tagged, it'll lock down Obito's ability to spam Izanagi. But god knows how many spare eyes he inherited from Madara's stockpile."
Unwinding the white bandages wrapped around his head, Kaien slowly blinked, opening his eyes for the first time in hours. Almost immediately, he felt the burn in his chakra. I've got enormous reserves for my age, but keeping two high-grade dōjutsu active at the same time is absolute insanity. "Then again, I'm barely ten years old... what did I expect?"
Forming the Rat and Ram hand seals in quick succession, he slammed a suppression seal over the Sharingan. The drain receded slowly, leaving him with a slight sigh of relief.
The Byakugan, however, remained open. That brought a whole different kind of torture. His mind was instantly flooded with an agonizing amount of visual information... walls melted away, bone structures became transparent, and chakra networks burned like neon veins in every direction.
"Oh... my fish save me," Kaien muttered under his breath, wincing as his gaze accidentally pierced through a few too many private rooms in the area. There are lot of things he is seeing which he shouldn't. "Right. Let's not talk about them."
Shifting his thoughts back to the current situation, he analyzed the war front. "Kiri is playing a waiting game, which fits them fine. But Konoha and Iwa uniting their forces... that's a nightmare scenario. Dan Katō's Spirit Transformation Technique is way too dangerous in times of war. But he was unusually cautious around Uncle Bee last time. That means he actually understands his own weaknesses of sealing."
Then he remembered the spare eye. "We still have one more Byakugan left. Giving it to either Grandpa or Uncle Bee would be the smartest play. Either of them could use it to keep tabs on Dan, spot his spirit form coming from miles away, and leak our strategic plans pre maturely."
~~
A short while later, Kaien found himself walking down the streets of Kumogakure's eastern district alongside Bee. This was the newly assigned compound for the Uchiha clan, naturally they had to buy the land and pay taxes.
The Uchiha were gradually settling into their new lives in Kumo. As the duo walked past, several clan members actually lowered their heads and gave meek nods of respect... a sight so uncharacteristic of the proud Uchiha that it almost looked alien.
"Grandpa mentioned he wanted to 'have a chat' with the Uchiha clan members when they arrived," Kaien mused, feeling sympathy for them. "I just hope he didn't give them permanent psychological trauma. He pulled the exact same terrifying stunt when the Chinoike clan joined us."
Bee with absolutely zero filter to his mouth, practically ruined the mystery by bursting into a rhythmic rap.
"The Raikage ain't no joke, Fought the whole Uchiha crew, beat 'em till their faces turned blue!
"No one died, no one bled, just a hundred ninjas fell asleep like babies in bed! Chakra drain is the name, Raikage is the Game"
The surrounding Uchiha flushed red, pulling their high collars up and ducking their heads in embarrassment.
Kaien rubbed his temples. "So that's how it went down. Grandpa challenged the entire clan at once and simply dragged the fight out until every last one of them collapsed from chakra exhaustion. Well... I suppose knocking everyone's ego out at the exact same time is one way to build unity. Now, nobody has the audacity boost when they all shared the same ridiculous humiliation. Who would have thought it would be this easy."
They finally reached the clan head's residence and stepped through the door, only to freeze dead in their tracks at the surreal scene unfolding in the kitchen.
Mikoto Uchiha was standing by the stove with her Mangekyō Sharingan. Why? Because the raw eggs she was cracking kept dropping tiny bits of eggshell toward the hot skillet. Using the terrifying, high-speed perception of her legendary eyes, she was moving her hands in a blinding blur, picking every micro-fragment of shell out of mid-air before it could touch the pan.
Out in the living room, One grown men and other three not so much... Fugaku, Itachi, Shisui, and Sasuke... sat around the table in silence. They weren't moving. They were barely even breathing.
Mikoto deactivated her eyes with a soft blink, her terrifying aura melting into a sweet smile as she turned around. "Breakfast is ready, everyone!"
Hearing footfalls at the door, she perked up. "Oh my, we have guests! Please, sit down! Let me whip up another batch for you two!" She raised a hand, her irises stirring as if to reactivate her Mangekyō once again.
In perfect unison, the four Uchiha men turned their heads toward the entrance in agonizingly slow motion. Their eyes offered a desperate plea for help.
Kaien took a step back, sweating nervously. "Please... don't trouble yourself, Mikoto-san."
~~
A/N: Protecting Sharingan is a very important step, it would prevent Obito from stockpiling sharingan for Izanagi like he did in canon. Now that he missed the Uchiha clan fight in Konoha, he could not collect any sharingan. Most of the Sharingan of the dead, were taken away by fellow Uchiha and Danzo's root.
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