IN NARUTO AS KURAMA

"Ding! Congratulations to the host for successfully traveling through time. I am your system. Do you need anything? Don't worry, others can't see me. You just need to talk to me in your mind."

A sharp yet deceptive voice rang in Shiro's ears. An elf-like figure materialized before him, glowing faintly.

At this moment, Shiro's hair stood on end. He mentally roared, "What the hell?! Other people travel through time and get to be princes, Uchiha prodigies, or Hyuga heirs! Why the hell did I become the Nine-Tails? And not even the full Kyuubi—just the Yin half!"

The system elf, visibly flustered, stammered, "W-well, the origin of the system wasn't sufficient, so there was a slight deviation when you crossed into this world. This... this is the result. But everything else is fine!"

Shiro's face darkened, resignation settling in. He sighed and looked at the elf with disappointment. "Fine. Tell me, what's the point of this useless system of yours?"

"Hey! Watch your tone!" The elf puffed up indignantly. "Let me show you how awesome your system is!"

With a dramatic gesture, the elf vanished into thin air, replaced by a booming, majestic voice. "This is the invincible and super-handsome Sign-In System—the latest innovation from our system company! Our goal: to inspire the host to become the most badass person—no, fox—alive!"

Shiro could only roll his eyes at the over-the-top proclamation. "Great. Does this amazing system at least have a beginner's gift package? Or are you throwing me straight into hell?"

"Of course!" The elf returned, crossing its arms. "Congratulations! You've received a newbie gift package. Would you like to open it?"

"Open it."

"Congratulations! You've obtained: Nine-Tails Chakra (Yin), the Invincible Sealing Technique, External Incarnation, and an improved Nine-Tails bloodline."

Shiro's eyebrow twitched. "That's it?"

"Yes, that's it," the elf replied unapologetically.

(╯□╰ )

Suppressing his irritation, Shiro took a deep breath. "Fine, fine. I'm just a regular Nine-Tails, so what's the point of the rest? Seriously, what kind of useless system are you?"

The elf bristled. "Useless? I'll show you useless! The Invincible Sealing Technique lets you master every sealing jutsu in the Naruto world. External Incarnation? That's on par with Sun Wukong's clones—far superior to Kage Bunshin. And your improved Nine-Tails bloodline? Your body isn't just chakra anymore; you're a flesh-and-blood Nine-Tails now!"

Shiro waved a paw dismissively. "Whatever. Let's just start by absorbing the Nine-Tails Chakra."

A massive cloud of sinister red chakra flooded the dungeon. Shiro devoured it in a single gulp, without hesitation. His form began to grow exponentially, shaking the very foundations of the Eight Trigrams Seal. Moments later, his transformation completed.

He was the full-fledged Kyuubi.

But just as Shiro began reveling in his newfound strength, a voice boomed in his mind. "Who are you?! Get out of my body, or I'll devour you!"

Shiro smirked. "Oh? The remnants of the original Kyuubi's consciousness? How quaint." With a cruel grin, he crushed the lingering will of Kurama with ease, completely subduing it.

Power surged through Shiro's body. "This power... The Sage of Six Paths really did spoil this fox. Incredible."

He focused inward. "Integrate the bloodline, master External Incarnation and Invincible Sealing Technique."

This time, there was no dramatic explosion of energy. The upgrades occurred subtly but with immense impact. As the improved Nine-Tails bloodline fused into his being, Shiro felt his body burn, reshaping itself into something far superior. When the process ended, the system chimed again.

"Ding! Congratulations! Your bloodline has been upgraded to the Nine-Tailed Fox bloodline. You also have one free sign-in opportunity."

"Use it."

"Sign-in successful! Congratulations! You've obtained the Eternal Mangekyō Sharingan. Have fun playing with your Gundam!"

Shiro blinked. "Eternal Mangekyō? For the Nine-Tails? This just keeps getting better." A sly grin spread across his face as a kaleidoscope pattern momentarily swirled in his eyes before vanishing.

He turned his attention to the Eight Trigrams Seal before him. "This flimsy seal? Not even a challenge." With a casual swipe of his paw, the prison vanished, revealing a complex, glowing magic circle beneath it. Shiro stretched out on the floor, finally relaxing.

"Ah, much better. Though I can't leave just yet. If I do, this brat Naruto will probably die. Not to mention those old bastards like Obito, Danzo, and Hiruzen will be all over him."

Settling in, Shiro glanced at the shadows in the dungeon. "I know you're there. Come out already."

No response.

Without warning, his chakra surged violently, shaking the sealed space. The oppressive aura summoned Minato Namikaze, who appeared within the seal, glaring at Shiro.

"Nine-Tails! Don't go too far!" Minato's voice rang with authority.

Shiro raised an eyebrow. "Too far? If I really wanted to, your precious son would go boom in the next second."

Minato stiffened at the cruel remark. "Nine-Tails, I know it was wrong to seal you, but my son is innocent. Please, spare him. Take my life instead."

Shiro burst into laughter. "Oh, how noble! Touching, really." With a wave of his paw, a large leather sofa materialized. Shrinking down to a smaller fox form, he curled up on it and gestured for Minato to join him. "Sit. Let's watch together and see how your son survives the next five years. You're wasting your sentiment on a place like Konoha."

Reluctantly, Minato sat beside the uncharacteristically relaxed Nine-Tails, his expression conflicted as he glanced at the dungeon's darkness.