Spar

Sitting at the table, an awkward atmosphere enveloped the scene. Naruto observed the silver-haired teenager with lazy black eye, his other left eye concealed by his forehead protector and a mask hiding his lower face. He then turned his attention to Mirai, who was occupied with cooking, deftly controlling the knives and efficiently handling the ingredients from a distance.

"Uncle, who's this weird ninja? Is he so ugly that he has to hide his face?" Naruto asked loudly.

Mirai chuckled at Naruto's bluntness, never pausing in his cooking. "Naruto, his name is Kakashi. He's not weird, just unique. And no, he's not hiding because he's ugly."

Kakashi's sole visible eye twitched, being called weird and ugly in their first meeting, directly to his face.

Mirai set down his apron and turned to Naruto with a gentle smile. "Naruto, Kakashi is a renowned genius in the village. He became a jonin at a very young age and has accomplished many things."

Mirai's smile widened as he continued. "Kakashi was also Minato's disciple."

Naruto's eyes lit up with excitement. "Were you my dad's student?" He asked, his eyes alight.

Taken aback by Naruto's enthusiasm. Kakashi quickly composed himself and replied. "Yes, I was in Minato-sensei's team."

Mirai immediately intervened, saying. "As he was taught by your dad, he will be responsible for teaching and training you when I am busy."

Naruto beamed a huge smile at the still bewildered Kakashi. "Really? Kakashi nii-chan!"

Kakashi could only nod absentmindedly, still baffled. He muttered. "Kakashi nii-chan?"

…

After finishing dinner, where Naruto spent the entire time trying to glimpse Kakashi's face only to fail each time. Kakashi quickly excused himself and bid goodbye to Mirai and Naruto. 

Not long after, as he walked away from the house, he sensed a presence and turned to find Mirai leaning against a wall, having left a clone behind to finish up.

Mirai grinned at him. "I expect you not to neglect Naruto's training."

Kakashi sighed tiredly. "I didn't have much choice to begin with."

Mirai's expression turned serious as he said. "Follow me." Before vanishing, leaving Kakashi little time to respond.

Kakashi trailed behind him, his curiosity piqued. They soon arrived at a familiar, nostalgic, yet haunting place, the third training ground. Memories flooded Kakashi—warm recollections of training with his team mixed with the hollow ache of being the sole survivor.

Mirai stood in the center of the training ground, his back to Kakashi. Turning to face him, a small, knowing smile curled on his lips. "Since I returned to the village after three years, it's only natural for me to check your progress on behalf of your teacher."

Kakashi didn't reply verbally but instead lifted his forehead protector, revealing his Sharingan, and swiftly unsheathed the ANBU's short sword from his back, which he had previously hidden.

Mirai watched him calmly, his hands in his pockets, appearing relaxed. But this nonchalant posture didn't fool Kakashi. His honed senses, sharpened through the war and years of ANBU's missions, kept sending signals, warning him of the beast he was facing.

Bracing himself, he attacked. Mirai, responding with lightning reflexes, pulled a kunai from his pouch, opting not to use his Mercury techniques to keep the fight grounded.

Kakashi's vertical swing came down with force, but Mirai parried it effortlessly with his kunai, sparks flying from the clash. Mirai tilted his head sideways, narrowly avoiding the kunai Kakashi hurled with his other hand.

They separated momentarily, both assessing each other. Kakashi rushed at Mirai again, his Sharingan predicting Mirai's movements. He unleashed a flurry of strikes. However, Mirai met each blow with calm precision, his movements fluid and controlled.

Kakashi's sword swung in a wide arc, aiming to cut through Mirai's defenses. Mirai stepped back just enough to avoid the blade, using his kunai to deflect the strike, redirecting Kakashi's momentum. As Kakashi tried to capitalize on the opening, Mirai sidestepped, letting Kakashi's follow-up thrust miss by inches.

Kakashi, realizing that each attempt to break trough will be countered with minimal effort and that brute force wouldn't suffice, switched tactics. He feinted a high strike, then twisted mid-air, aiming a low slash at Mirai's legs. 

Mirai anticipated the move, leaping gracefully to avoid the blade and countering with a spinning kick that Kakashi barely blocked with his forearm.

Kakashi's forearm throbbed from the impact of Mirai's spinning kick. As he landed, his breath quickened, and he panted heavily. Mirai, however, remained composed, his eyes sharp and assessing.

"You're only using the standard [ANBU Kenjutsu]. It focuses on overwhelming the opponent with a series of swift slashes—practical but not sophisticated." Mirai noted, his voice calm but piercing. "Did you really abandon what your clan and father spent their lives cultivating and strengthening? The [ Hatake Clan Kenjutsu]. Did you truly forsake their honed blade?"

Kakashi gritted his teeth and charged again, his Sharingan moving erratically, analyzing every possible move. Mirai's eyes glinted slightly. "You're too reliant on your Sharingan. It's become a shackle, limiting your growth and rapidly draining your chakra."

Determined to prove himself, Kakashi launched a series of rapid strikes. He feinted, pivoted on his heel, and swung his sword in a wide arc. Mirai ducked under the swing, stepping in close and using the momentum to push Kakashi back with a well-placed shoulder strike. Kakashi stumbled, quickly regaining his footing, but Mirai was already in front of him, kunai poised defensively.

"Is that all you've got?" Mirai asked.

Kakashi's frustration grew. He swiftly completed the sequence of hand seals and gathered his chakra, forming a [Chidori] in his hand. The crackling energy illuminated the training ground, the high concentration of electricity producing a sound of many birds chirping. With a burst of speed, he dashed toward Mirai, aiming to break through his defenses.

Mirai stood his ground, watching Kakashi's approach. At the last moment, he sidestepped, grabbing Kakashi's wrist and redirecting his hand into the ground. The impact created a small crater, sparks flying around them. 

Before Kakashi could recover, Mirai spun him around, disarming him and pinning him to the ground with a kunai at his throat.

"Is this your best?" Mirai asked, his voice steady. "Or do you have more to show?"

Kakashi, breathing heavily, clenched his jaw, his resolve wavering.

Mirai, freeing Kakashi and retreating, suggested. "Don't be rigid. Apply shape transformation to your [Chidori]. Create variations suitable for different situations."

Kakashi's eyes widened, a spark of understanding igniting within him. "I'll try."

Standing up and gripping his short sword once more, Kakashi didn't rush this time. He took his time concentrating, before forming his hand seals with precision.

"[Raikiri]" He announced. Lightning chakra flowed from his hand into his blade, causing the tantō to radiate and emit a high-pitched chirping sound.

Kakashi held his sword steady, taking a deep breath before charging at Mirai with a speed that surpassed his previous attempts. In an instant, he was upon Mirai.

"[Thunder Thrust]" He called out. Holding his blade aloft, Kakashi drew it back, super-condensing the lightning chakra into its tip. With a powerful thrust, he aimed his tantō directly at Mirai.

Mirai stood his ground, not attempting to dodge or evade. Instead, he let Mercury engulf his side protectively, meeting the concentrated lightning head-on. The impact was tremendous, the energy arcs crackling around them as Mirai's feet skidded slightly along the ground, leaving scorched marks.

Kakashi, his chakra reserves utterly depleted, collapsed to the ground, his vision darkening and consciousness slipping away. In his last moments of awareness, he heard Mirai's steady voice.

"That was a good hit, Kakashi. I took it head-on without evading, and I received your determination."