In Naruto Trying to become a Saiyan from Kumogakure

Mito took a deep breath, her gaze steady as she addressed Tsunade. "Alright, Tsunade, listen carefully. What I'm about to do involves integrating an array of Four-Symbol Seals within your Yin Seal. This will create a specialized sealing space, one that expands the chakra storage of the Yin Seal from a purely physical reserve into a vast spiritual dimension. With Kurama's presence and the stabilizing effect of the Four-Symbol Seals, this space will grow over time, becoming an immense reservoir capable of holding a tremendous amount of chakra, both yours and Kurama's."

She placed a reassuring hand on Tsunade's shoulder, her expression both firm and gentle. "In the future, your Yin Seal will serve as a bridge between your physical body and this spiritual space. Your body will continue to store your personal chakra as it always has, but this new space will hold both your chakra and Kurama's. With time, you'll be able to access this connection freely, drawing on Kurama's chakra as if it were an extension of your own. However, the key to accessing it lies in your relationship with him. You must learn to get along with Kurama, Tsunade." Mito's lips curved into a small smile. "By the way, his name is Kurama, not just 'Nine-Tails.' He has watched you grow since the day you were born, he is your elder, so treat him with the respect he deserves."

Although Tsuande was surprised by the way Mito talked about 9-tails, she accepted it as if it was her orders. As she or her grandfather never disobeyed the serious Mito.

With that, Mito began the sealing process. The air around them pulsed with power as intricate formulae of the Four-Symbol Seals spread across Tsunade's Yin Seal, weaving into it like invisible lines. Meanwhile, within Mito's own seal space, Kurama stirred, his massive form shifting as he prepared for what was to come.

A deep, rumbling growl resonated through the chamber as Kurama performed the separation along with Mito's help. She extracted more than half of Kurama's chakra, along with his entire consciousness, and guided it into the newly created spiritual space within Tsunade's Yin Seal. What remained in Mito's body was a mass of pure chakra, still taking the shape of the Nine-Tails, yet eerily hollow.

As the process completed, the distinction became clear, the Kurama leaving Mito's body was vibrant and alive, his fiery eyes filled with awareness, while the husk left behind was merely a shadow of what he once was. An empty shell of chakra without sentience, existing only as residual energy.

Mito exhaled, her strength wavering for a brief moment before she steadied herself. The transfer was complete. Tsunade now carried the key to a power unlike any before, but whether she could master it would depend entirely on her ability to forge a bond with Kurama.

For Kurama, separating his chakra from himself wasn't difficult, after all, his chakra was an extension of his existence. However, splitting his full chakra into two nearly equal halves posed a much greater challenge. His chakra naturally sought to merge back together, drawn by its own immense energy. The process required an external force, Mito to intervene and forcefully sever the attraction, ensuring the division remained stable, and was possible.

Tsunade had followed along with Mito's arrangement, trusting in her grandmother's wisdom, yet she hadn't fully grasped the depth of the plan. Now, however, she found herself standing within her newly created spiritual seal space, face to face with the mighty Nine-Tails himself. The towering beast loomed over her, his fiery eyes regarding her with a mix of curiosity and skepticism.

For a moment, she simply stared before a thought struck her, causing her to blurt out, "Wait… if a Tailed Beast is extracted, doesn't that mean Grandma will die?!" Then, as if suddenly remembering something far more important, she grinned and added, "Oh, by the way, nice to meet you, Kurama! I'm the best gambler in the world Tsunade!!"

Kurama narrowed his eyes, then let out a scoff half amusement, half exasperation. "Yes, I can see that. You're even more talented than Hashirama at gambling, truly a rare ability. Perhaps it's some strange manifestation of the all encompassing natural energy a talent in its own right."

His tails swayed lazily before he continued, his voice laced with an air of superiority. "As for your grandmother, don't worry. What remains inside her isn't actually me, but rather half of my chakra, nothing more than a husk that retains my form. I can control it remotely, but it's just raw energy, devoid of my will. That half will stay within Mito and, when the time comes, be passed on to Konoha's next Jinchuriki."

Tsunade frowned slightly. "But wouldn't that still be dangerous?"

Kurama let out a low chuckle. "For them, maybe. That chakra will slowly regenerate over time if it's used, but without my direct approval, anyone who tries to wield it will struggle. Only those strong enough to overcome the hatred and raw emotions embedded within it will be able to use even a fraction of its power. Otherwise, it will act like a provoked beast, wild, violent, and uncontrollable. But don't worry," he added with a smirk, "humans already think of us Tailed Beasts as mindless monsters, so it won't make much of a difference."

His smirk grew into something almost smug as he continued, "Besides, I can connect to that husk of my chakra whenever I want. As long as that chakra remains in Konoha, I'll always know what's happening there. So, in a way, they may think they have sealed a beast, but in reality, a part of me will always be watching."

As Tsunade returned to the physical world, she was immediately overwhelmed by the immense power radiating from her grandmother. It was unlike anything she had sensed before, a vast and overwhelming presence that made the very air feel heavy with raw energy. Inside her mind, she heard Kurama's voice, his tone carrying a rare note of acknowledgment.

"Your grandmother is strong enough to fully wield half of my chakra," he stated. "And with my approval, combined with her naturally immense reserves, she can match my chakra ratio perfectly, achieving a true synchronization. This allows her to enter the strongest form of my chakra mode."

There was a moment of silence before he continued, his deep voice tinged with something close to pride. "Unlike before, when she could only forcefully draw on my chakra in a crude, unstable manner, this is an entirely different level. The power she wields now is countless times stronger than what she could achieve before."

In that moment, Mito had fully entered the state that would later be known as Kurama Mode with 9-tails eyes in her pupil, an enhanced and perfected version of the crude Nine-Tails Mode she had previously accessed. In this form, her strength had skyrocketed beyond the level of ordinary shadow. If before she was already formidable, now she had ascended to a level that could only be described as super-shadow, a realm where only legends like her husband stood.

Kurama spoke again, his words both reassuring and foreboding. "You don't need to worry about Konoha's safety. I have no idea if the next Jinchuriki will even be able to use my chakra properly, let alone access a weaker version of this mode. But right now, with my power fully supporting her, your grandmother has truly surpassed the level of ordinary Kage. She has reached a power comparable to your grandfather. So, if you were worried about leaving the village, rest assured there is no one here who can challenge her."

Tsunade's eyes gleamed with excitement as she took in the sheer presence of her grandmother, bathed in golden chakra, her form radiating divine-like power. Unable to contain herself, she turned her thoughts back to Kurama and exclaimed eagerly, "Respected Elder Kurama, I will treat you nicely and cooperate! Can I also become as strong as Grandma?!"

Inside her spiritual space, Kurama let out a scoff, his massive tails swaying behind him. "Hmph. You'd better treat me right. Although you aren't a true Jinchuriki and won't die if I leave your body, losing me would still cause you plenty of trouble. Your chakra and physical constitution aren't as monstrous as your grandmother's yet, so you can't fully synchronize with my chakra the way she can."

He paused before adding with a smirk, "Maybe, with time and effort, you can barely sustain the weakened version of this power."

His eyes gleamed with amusement as he delivered his final words. "So keep working hard, kid."