The next morning, before dawn broke across the village, Kakashi led Sasuke to the isolated cliffs outside Konoha's training perimeter. The wind blew strongly there, and the wide open sky above allowed for large-scale ninjutsu without risk of collateral damage.
"From here on," Kakashi said, "you'll be training under chakra strain. Your Mangekyo's power will tempt you to overuse it, but if you do, your eyesight will begin to fail."
"I understand. I won't waste time." Sasuke stood quietly as he seriously listened to Kakashi.
He activated his Mangekyō Sharingan again, the curved pinwheel spinning with eerie grace. He felt that now-familiar pressure on his optic nerves, but he bore it calmly.
Kakashi made a seal with his hand, and three shadow clones formed in a triangle around them.
"Each shadow clone has a Jonin-level strength. You'll face them using only your Mangekyō abilities. Start." Kakashi said.
The first clone dashed forward, launching shuriken in a wide arc. Sasuke didn't move. His left eye pulsed, Amaterasu erupted mid-air, the black flames incinerating the shuriken before they reached him.
With his right eye, Kagutsuchi twisted the flames into spikes and launched them directly into the charging clone's chest. It dispersed instantly.
The second clone struck from behind. Sasuke didn't even turn. A wall of black fire spun into existence behind him, shaped like a curved wing, protecting him from the strike. He turned, manipulating the edge of the wing to spiral outward like a blade, and sliced through the clone's midsection.
"You're shaping it better already." Kakashi raised an eyebrow.
The final shadow clone flashed underground. Sasuke closed his eyes briefly, feeling the chakra under the soil. He opened them again, narrowed. With a quick motion, he pointed his right index finger downward.
A narrow spike of Amaterasu shot straight into the earth, and the third clone burst apart as it tried to ambush him.
Sasuke took a step back, breathing heavier now. His Mangekyō spun faintly slower than before.
"Rest," Kakashi ordered. "Not too long, only long enough for your vision to recover. I'll be monitoring your chakra flow."
"I can't afford to waste time." Sasuke sat on a nearby rock, scowling.
"And you can't afford to go blind either," Kakashi replied firmly. "Let the eyes rest between sets. This isn't genin-level training anymore."
Sasuke grunted but obeyed.
Elsewhere in the village…
Naruto sat on the roof of their house, a pout on his face as he watched the direction Kakashi and Sasuke had gone.
"He didn't even invite me," he muttered, chewing on the edge of his dango stick. "Stupid Sasuke with his stupid red eyes…"
{Jealousy doesn't suit you, brat,} came the deep, rumbling voice inside him.
"Shut up, Kurama. I just don't like being left out, that's all." Naruto rolled his eyes.
{Hmph.} Kurama's tone oozed amusement. {You feel it, don't you? That change in him. That scent of blood and darkness. His chakra isn't the same anymore.}
Naruto frowned. He didn't want to admit it, but… it was true. Ever since Sasuke had awakened that stupid Mangekyo thing, he felt more distant, more intense. Like a blade that had finally decided to cut.
"He's always been intense," Naruto mumbled. "But now it's like… he's serious."
{His eyes,} Kurama growled, {they are like his ancestors'. Uchiha Madara. The same hatred. The same pride. The same hunger for power.}
"You're saying Sasuke looks like some Madara you know?" Naruto blinked.
{Not looks. Feels. The chakra behind his eyes twists the air. Don't take it lightly, kid. Mangekyo Sharingan is not some toy. It is a weapon shaped by hatred and grief. One that often burns its own master.}
Naruto leaned forward on his knees, watching the distant training cliffs. "He's not some Madara or anything. Sasuke's just trying to get justice for his family. Maybe… the way I want to become Hokage."
{Just don't forget to watch him. Closely. Friends can fall the fastest when they walk in the shadows.} Kurama's voice quieted for a moment, then answered,
"I'm not gonna lose to him… or let him fall either, Believe it!" Naruto clenched his fist.
{Then get stronger, fool.}
After a short break, Sasuke was back on his feet. Kakashi had replaced the clones with real training dummies reinforced with chakra seals.
"This time," Kakashi said, "I want you to shape Kagutsuchi defensively and offensively at the same time. One hand guards, one attacks. Do it under pressure."
Sasuke exhaled slowly and activated his Mangekyō again.
The first dummy fired a series of fireballs. With his left hand, Sasuke blocked them with a swirling black flame dome. With his right, he shaped a spear from the same black fire and launched it, piercing the chest of the second dummy. It collapsed, scorched.
"More," Sasuke demanded, sweat dripping down his chin. His breathing was heavier now, and his vision was beginning to blur at the edges.
Kakashi didn't stop him. He knew Sasuke needed to reach his limit.
Another attack came, and this time, Sasuke summoned two curved flame blades around his forearms, using them to parry incoming kunai while sending tendrils of Amaterasu toward the third dummy. It tried to dodge, but Kagutsuchi shifted the flames mid-flight, burning it from behind.
He dropped to a knee.
"That's enough." Kakashi stepped forward quickly and placed a hand on Sasuke's shoulder.
"Just… a little more." Sasuke gritted his teeth.
"No. You're pushing it. Your optic nerves are already inflamed." Kakashi's voice was firm.
"Fine." Sasuke finally nodded, breathing hard.
As they began walking back toward the village, Kakashi spoke again. "You're getting there."
Naruto lay in bed, his eyes open, staring at the ceiling. The memory of Sasuke's Mangekyō burned in his thoughts like a ghost.
"I gotta catch up," he whispered.
{Then stop whining and start moving," Kurama growled inside him. {The Uchiha boy is not slowing down for you.}
"I'll find my own way," Naruto whispered. "Even if I have to fight him one day."
{Just make sure you're ready… because he already is.} Kurama was silent for a moment, then said.