Ren suspected that his inability to master the Flying Thunder God Technique was partly due to his natural physique.
Reaction speed, information-processing ability, spatial awareness, chakra control, and physical coordination were all essential. A weakness in even one of those areas could make the technique impossible to learn.
Those innate qualities were probably the most important requirements.
Otherwise, Hiruzen Sarutobi should have been the first person to master the Flying Thunder God after the Second Hokage's death. He had personally studied under Tobirama Senju, carried the title of Professor of Ninjutsu, and was rumored to have learned every technique in Konoha.
Yet even Hiruzen had failed to inherit the technique.
The village had been forced to wait until Minato appeared before the Flying Thunder God once again became a terror on the battlefield.
Ren could only hope that Minato possessed a suitable method for training his reaction speed. If even the future Yellow Flash couldn't help him overcome that weakness, Ren would have to consider a more dangerous alternative.
Once he became strong enough, he could find a way to steal Kumogakure's Lightning Release Chakra Mode.
That technique strengthened the user's body and stimulated the nervous system with lightning chakra, dramatically increasing both speed and reaction time. Obtaining it from the Hidden Cloud would be difficult, but not necessarily impossible.
That plan belonged to the distant future.
Although development of the Death Mark had temporarily encountered a bottleneck, Ren had recently received another piece of excellent news.
His Great Fireball Technique had finally broken through.
After completing the Rectification mission, its favorability had already exceeded ninety. Another week of relentless training had allowed Ren to overcome the final barrier and enter a completely new realm.
A familiar notification appeared before his eyes.
Great Fireball Technique favorability increased by 2!
Great Fireball Technique: 100/100 — Heart-to-Heart Connection
Stage rewards obtained: Four
Physique increased by 4.
New Trait—Heart of Burning Ash: Your affinity with Fire Release chakra has increased significantly. The power of all Fire Release ninjutsu is enhanced by 240 percent from its current foundation. By consuming large quantities of additional chakra, you may continuously increase the temperature and burning power of the Great Fireball Technique until it becomes a purgatorial flame that cannot be extinguished by fierce winds or torrential rain.
Ren stared at the notification.
"Two hundred and forty percent…"
It was exactly as powerful as he had hoped.
More importantly, the enhancement wasn't restricted to the Great Fireball Technique. Every Fire Release technique Ren possessed would receive the same enormous increase in power.
The moment the trait activated, the fire-natured chakra within his body changed.
It became extraordinarily lively yet strangely obedient, flowing through his chakra network with almost no resistance. For a brief moment, Ren felt as though he could ignite the air itself with nothing more than a thought.
Of course, that was merely an illusion created by his dramatically improved affinity.
Unlike the traits granted by the Three Basic Techniques, Heart of Burning Ash didn't increase his casting speed. Ren still needed to form the appropriate hand seals before releasing Fire Release ninjutsu.
Fortunately, the Great Fireball Technique required only six seals. After practising the sequence countless times, Ren could complete it in roughly one second.
The lack of instant activation was a small inconvenience compared with the overwhelming increase in destructive power.
Then there was the second part of the new trait—the ability to continuously increase the Great Fireball's temperature.
Ordinary flames generally ranged from several hundred degrees to slightly above one thousand. That level of heat was dangerous to civilians and low-ranking ninja, but experienced shinobi could protect themselves with chakra or counter it with defensive ninjutsu.
What if Ren raised the temperature of his flames to six thousand degrees?
He paused.
No, six thousand still didn't sound ambitious enough.
He would begin with a small goal.
Ten thousand degrees.
Once his Great Fireball reached that temperature, the Uchiha clan's legendary black flames would have to surrender their title.
Amaterasu would become known as the Little Great Fireball Technique.
The thought alone nearly made Ren laugh.
He stood at the center of the training ground and took a deep breath. Kakashi, Obito, and Rin were practising separately nearby, but none of them initially paid much attention to him.
Ren raised his hands.
His fingers blurred through the familiar sequence.
"Snake, Ram, Monkey, Boar, Horse, Tiger…"
His chest expanded as fire-natured chakra surged into his lungs.
"Fire Release: Great Fireball Technique!"
Boom—!
Flames erupted from Ren's mouth with the roar of an explosion.
An enormous orange fireball burst into existence and swept across the training ground. It rapidly expanded until it reached seven or eight meters in diameter, becoming almost as large as a small house.
The raging sphere of flame surged into the sky, turning the peaceful training ground crimson.
Even from a distance, it resembled a miniature sun rising above the trees.
Ren didn't stop.
He continued pouring chakra into the technique.
The inferno's color gradually changed. Orange deepened into bright yellow, then faded into a blinding white as the temperature climbed.
Heat rolled across the field in violent waves.
The air surrounding the fireball twisted and rippled, while moisture evaporated from the ground beneath it. Nearby grass curled, blackened, and began to smoke without the flames ever touching it.
Kakashi and Obito stopped their ninjutsu training at the same time.
Both turned toward Ren, shock breaking through their usual expressions.
Rin's Water Clone collapsed into a splash as her concentration shattered. She stared at the enormous sphere of white fire with her mouth slightly open.
"No way…"
Was that really the Great Fireball Technique?
Whose Great Fireball could possibly become that large?
Had Ren fed it some kind of super fertilizer?
Obito slowly looked at the fireball he had just produced.
His own technique had created a sphere nearly three meters in diameter, which was already exceptional for someone his age. In terms of size and power, Obito's Great Fireball was comparable to—or even stronger than—the one Sasuke Uchiha would produce at the same age.
A moment earlier, Obito had been rather proud of it.
Now, his fireball looked like a candle flame beside Ren's artificial sun.
The comparison was so brutal that Obito briefly wondered whether they were using the same technique.
What made the situation even worse was that Ren had deliberately restrained part of his power.
After maintaining the technique for several more seconds, Ren finally stopped supplying chakra. The enormous fireball continued flying before gradually breaking apart in the distance, leaving shimmering waves of heat in its wake.
He lowered his hands and rubbed his cheeks.
Even with his increased Fire Release affinity, the returning heat had left his skin burning.
Ren carefully reviewed the results.
Flames generally became visibly white at extremely high temperatures, while hotter flames could take on a blue hue depending on their composition. Judging by the current color and behavior of his technique, Ren estimated that he could maintain temperatures below two thousand degrees with reasonable stability.
Going beyond that point would become increasingly difficult.
Chakra consumption rose far faster than the temperature.
At first, the relationship felt like a power function, though Ren couldn't rule out the possibility that it eventually became exponential. He would need to conduct more controlled tests and record the results before determining the exact pattern.
If he could establish a reliable formula, he would know precisely how much chakra was needed to reach a particular temperature.
That would allow him to balance destructive power against efficiency instead of recklessly pouring chakra into every attack.
Even without further experimentation, the results were already astonishing.
A Great Fireball of this scale could no longer be stopped by two ordinary chūnin-level Water Release techniques. It would probably require three or four working together to extinguish it completely.
Once the Great Fireball's increased temperature was considered, even experienced ninja would struggle to defend against it directly.
Ren was delighted by the new trait.
The Great Fireball Technique appeared equally excited.
Its cheerful voice suddenly rang inside his mind.
Great Fireball Technique: Hehe! So this is what it feels like to share a heart-to-heart connection with Ren. My entire body feels so light! I'm not afraid of anything anymore! Can the Clone Technique do something like this?
A second voice responded immediately.
Clone Technique: Why are you dragging me into this again? It's only a Heart-to-Heart Connection. The three of us reached that stage with Little Ren ages ago.
Great Fireball Technique fell silent for half a second.
Clone Technique continued in a deliberately mysterious tone.
Clone Technique: Besides, the three of us share a much deeper relationship with Little Ren. Over the last few days, he has repeatedly taken us into a small room, turned off the lights, and then…hehehe.
Great Fireball Technique: ???
Phoenix Sage Fire Technique immediately leaned into the conversation, practically glowing with curiosity.
Phoenix Sage Fire Technique: What happened next? Is there some scandalous secret? Hurry and tell me everything!
The other techniques offered their own reactions.
Water Release: Wild Water Wave: What a shallow conversation.
Substitution Technique: Staring.
Water Formation Wall: Staring.
Ren's expression went blank.
How could his own ninjutsu spread such outrageous rumors about him?
What did Clone Technique mean by taking the three of them into a dark little room?
After thinking about it, Ren finally understood.
The "small room" was probably the Death Mark, while "turning off the lights" referred to activating Phantom Stage.
The description wasn't technically false, but the way Clone Technique phrased it made the entire situation sound thoroughly indecent.
Ren was about to demand an explanation. He wanted to know when these supposed secret meetings had happened and exactly what Clone Technique believed they had done together.
Before he could begin the interrogation, a golden flash illuminated the training ground.
The light faded, revealing a familiar figure.
Obito's previous shock vanished instantly.
"Minato-sensei! You're here!"
Minato smiled gently as he looked over his students. "I am. How is everyone's training progressing today? Have any of you encountered problems?"
Ren had several questions about the Death Mark, but he didn't mention the technique in front of Kakashi, Obito, and Rin.
The ability was one of his most important hidden cards. Until he fully understood its strengths and weaknesses, he had no intention of revealing its existence unnecessarily.
Instead, he asked Minato several general questions about chakra-control training.
Obito and Rin then took turns explaining the difficulties they had encountered with their own ninjutsu. Minato listened patiently and answered each question, occasionally demonstrating a hand position or correcting their understanding of chakra circulation.
Once everyone had received guidance, Minato reached into his flak jacket and removed a mission scroll.
"I also came to inform you about Team Minato's next assignment."
Obito straightened immediately.
Minato opened the scroll and continued, "It is a C-rank mission. We've been asked to escort several nobles from the Land of Fire to the Land of Tea, where they intend to visit relatives."
He looked toward Ren, Rin, and Obito.
"The journey is longer than our previous escort mission, so we will likely be away for several additional days. Return home and prepare your supplies today."
Obito's excitement instantly collapsed.
"Another escort mission?" he complained. "Do these nobles have nothing better to do? A war is about to begin, yet they're still running from one country to another!"
Ren released a quiet sigh.
"War is a problem for ninja, not nobles. Besides, if they stopped travelling and hiring escorts, how would we earn money?"
Obito opened his mouth but found no answer.
Minato rolled up the mission scroll, his gentle smile unchanged. To anyone else, escorting a few nobles through the Land of Fire sounded routine.
But Ren had already completed one so-called routine escort mission.
This time, their destination was the Land of Tea—and he no longer trusted the word "routine."