After Minato left, Mutsuki looked at the Flying Thunder God Jutsu on his Panel, which still displayed as Beginner. He immediately clicked on the Ninjutsu Mastery scroll in his inventory.
Considering that powerful Ninjutsu would be difficult to practice, Mutsuki rarely used Ninjutsu Proficient scrolls. He only tested it when he first obtained them and later used a few on Medical Ninjutsu. The only Ninjutsu Mastery scroll remained unused.
Upon opening it, Mutsuki saw a large list of Ninjutsu. He only needed to click on any Ninjutsu and confirm, and the Ninjutsu would be upgraded to Mastery level. For Ninjutsu already at Mastery level, the Proficiency level would increase.
Mutsuki ignored the other Ninjutsu and quickly found the Flying Thunder God Jutsu with only one Proficiency point.
[Ninjutsu Mastery Scroll has been consumed, skill Proficiency level increased -- Flying Thunder God Jutsu (Mastery level: 1/15000)]
As soon as the points were allocated, a large amount of memories related to practicing Flying Thunder God surged into Mutsuki's mind. Problems he had once found difficult and hard to understand were instantly clarified, and he even had a sense of "Is that all there is to it?"
When Flying Thunder God reached Mastery level, Mutsuki's understanding of the technique reached a whole new level.
First of all, he could now confirm that "Returning Home Mutsuki" was possible. The Flying Thunder God had two major limitations in terms of movement distance: one was the sensing range, and the other was the Chakra amount.
If Mutsuki's sensing range could cover the entire Shinobi world, and his Chakra was sufficient to use Flying Thunder God anywhere in the world to return home, then "Returning Home Mutsuki" could become a reality. He could rest at home when tired and then attack again when his opponent wasn't prepared.
Of course, with that much Chakra, it's likely no one would be able to force Mutsuki back home anyway.
In addition to the two main limitations, there was another factor that affected the Flying Thunder God's distance and even the Chakra consumption: the Proficiency level of Flying Thunder God, which could be described as its "realm" in a more fantastical sense.
For example, if Mutsuki only had the Beginner-level Flying Thunder God, it would cost him 5,000 Chakra to move from point A to point B, and he wouldn't be able to directly teleport from point A to point C.
However, if Mutsuki reached the Proficient level of Flying Thunder God, it might only cost him 3,000 Chakra to move from point A to point B, and he could directly teleport from point A to point C.
At the Mastery level, the Chakra consumption would be even less, and the distance covered would be greater.
With this understanding of Flying Thunder God, Mutsuki formed a more reasonable guess as to why Senju Tobirama died while staying behind, rather than using Flying Thunder God to escape with Shimura Danzo and Sarutobi Hiruzen.
Although Senju Tobirama was a master of forbidden techniques and developed many of them, the techniques he created weren't necessarily perfect. For example, Impure World Reincarnation during Tobirama's time could only be used for self-detonation, but after Orochimaru's improvement, it could fully bring forth the abilities of the user in life.
Mutsuki speculated that Flying Thunder God was similar. In Tobirama's time, the technique consumed a large amount of Chakra, and using it with others only increased that cost. As a result, it could mostly only be used as a trump card in battle.
As for why reanimated Tobirama can easily bring people along, it may be related to the unlimited Chakra provided by Impure World Reincarnation.
As for who modified the Flying Thunder God in Konoha, it was definitely Minato.
After using the Mastery-level scroll, Mutsuki didn't stop. He used a Ninjutsu Proficient scroll on Flying Thunder God Jutsu.
[Ninjutsu Proficient Scroll consumed, skill Proficiency level increased—Flying Thunder God Jutsu (Mastery level: 168/15000)]
The Proficiency level increased slightly, and new training memories appeared in Mutsuki's mind, but they were fewer compared to the jump from Beginner to Mastery.
Mutsuki didn't hesitate and used up seven more Ninjutsu Proficient scrolls.
He had originally obtained thirteen Ninjutsu Proficient scrolls. Most were rewards from his disciples after Academy exams, while the rest were from improvement or training task rewards.
Mutsuki had used three before, and before adding points, he had ten Ninjutsu Proficient scrolls left.
[Ninjutsu Proficient Scroll consumed, skill Proficiency level increased—Flying Thunder God Jutsu (Mastery level: 1336/15000)]
The Proficiency level shot up by over a thousand, and Mutsuki's mind was flooded with many new insights.
Although the next level is still quite far, this number is not small. From Proficient to Mastery, it only requires 3,000 Proficiency levels, and 1,300+ Proficiency levels already accounts for nearly half of Proficient level.
Mutsuki didn't use the remaining two Proficient scrolls, keeping them for emergencies.
Looking at his Flying Thunder God with over 1,300 Proficiency levels at the Mastery level, Mutsuki was very satisfied. With his hard work to reach Beginner and the slight help from the Panel, the Proficiency level of Flying Thunder God was among the top of his skills. After reaching Mastery level, the Proficiency level of general skills becomes harder to increase, and high-difficulty Ninjutsu are even more so.
Mutsuki took out a Kunai, and with Chakra applied, a black character—"Master"—appeared on the Kunai.
Then, Mutsuki threw the Kunai and immediately used Flying Thunder God to move a short distance.
Since the space at home was too small to perform the technique properly, Mutsuki went to the training ground for testing.
With the support of Transparent World or the Lightning Chakra enhancement, there were no reaction issues. For short distances, it wasn't much different from Minato.
However, this Minato refers to Minato during his battles with the Jinchuriki. Mutsuki hasn't seen the current Minato in action, so it's difficult to compare.
But looking at the Panel, Minato has indeed made significant progress, both in terms of skill Proficiency levels and Chakra.
When Mutsuki first met Minato, Minato had only 40,000 Chakra. About half a year later, Minato's Chakra had increased to 47,600. Today, after using the appraisal skill, Mutsuki saw that Minato's Chakra had risen to 69,000.
This is why Mutsuki wants to take Nagato as his disciple. Nagato hasn't even reached his rapid growth phase, yet he already has so much Chakra. After he turns 18, his Chakra will likely increase even faster.
Of course, Minato's growth during his rapid phase is fast, but Mutsuki, with his cheats, grows even faster.
[Name: Mutsuki Yumi]
[Chakra: 104,400]
When Mutsuki first met Minato, Minato had 40,000 Chakra, and Mutsuki had only a little over 4,000. Now, after nearly two years, Mutsuki's Chakra has successfully surpassed six digits.
Once, Chakra was Mutsuki's weak point, but now, looking across all of Konoha, Mutsuki's Chakra is among the higher amounts.
Although this amount of Chakra is still not quite enough for Mutsuki's methods, it's already much better than before.
After completing the test, Mutsuki returned home and reorganized his upcoming plans.
Obito's life mission is about to surpass twenty points, so it can be pushed a little to gain rewards.
Perfecting the Yang Seal and developing accompanying Ninjutsu are daily must-do tasks, while studying Sun Breathing is relatively important.
Finally, the key task is figuring out how to perfectly become Nagato's sensei and guide his Chakra towards greater strength.
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