The retarded System's evaluation of his swordsmanship isn't low, but that doesn't mean his true strength is comparable to so-called Chunin or Jonin.
Most of the rewards given cannot be used because he doesn't have Chakra.
It's as humorous as throwing him into ancient times and giving him a submachine gun without any bullets.
Assuming a person has a great talent for shooting, the weapons they can use differ under different historical backgrounds.
Ordinary crossbows naturally cannot be compared to sniper rifles.
Perhaps both can achieve precise kills within a hundred meters, but five hundred or a thousand meters far exceeds the limit of the former.
The world's limitations are right here; Kiyokawa Izumi is naturally very interested in the so-called Eight Gates.
He doesn't think he can use it, but by studying the principles, could he create a budget version of a budget version?
Cultivating this Taijutsu also requires Chakra. Kiyokawa Izumi is different from Rock Lee; while the latter has no affinity, the former truly doesn't have that thing called Chakra.
As a transmigrator, he has a general idea of this Taijutsu—the setting is that there are Eight Gates in the body that suppress Chakra. Once the restrictions are lifted, Chakra can be released in an overload, granting power far beyond one's limits.
Kiyokawa Izumi, who is Innate-ly lacking this energy, is interested but wouldn't choose this Ninjutsu.
The same applies to techniques like the Flying Thunder God Technique.
Getting these is like getting a firearm without bullets; you can't use them and can only stare helplessly.
In the current situation, to achieve a qualitative change in strength, he can only choose rewards that don't rely on Chakra.
The Uchiha clan's inherited swordsmanship or the so-called Konoha Style—while their Sword Techniques are worth referencing—aren't completely devoid of Chakra usage.
Kiyokawa Izumi doesn't think learning these would raise his swordsmanship Rank by another level.
His Sword Technique, already tempered a thousand times, is on par with his elder brother's in terms of Rank; how could it be easily Breakthrough-n with just a simple reference?
'Since I can't awaken the Demon Slayer Mark, let's try the Breathing Technique from another world.'
Kiyokawa Izumi's breathing rhythm was undergoing a noticeable change.
「Dark Breathing Lv3→Lv4」
What he chose was naturally the Seven-Day Breathing Method; it was what he needed most right now, yet the System had yet to reward it to him.
There was a reason he kept calling it a retarded System.
It kept giving him impressive-sounding abilities that he couldn't actually use.
It would be better to be practical and give him less powerful abilities that he could actually use.
The so-called Seven-Day Breathing Method was created by the Sunagakure Ninja Rōshi. Simply put, it enhances physical functions through breathing—the special breathing rhythm and usage methods are worth referencing because this world is dominated by Breathing Techniques.
Breathing possesses miraculous capabilities.
As a vast amount of knowledge flooded his groggy mind, his mastery of Dark Breathing saw a significant improvement after referencing the Breathing Technique from the other world.
At this moment, the only limitation was that his physical constitution was fundamentally different from Rōshi's.
Ordinary humans in that world's setting can have up to 130 trillion cells, more than double Kiyokawa Izumi's—the world he is in is more similar to his previous life, where the cell count is normally around 40 to 60 trillion.
That's a two to three-fold difference.
The basic physical constitution is completely different.
Even if Kiyokawa Izumi could perfectly use the Seven-Day Breathing Method, he couldn't reach Rōshi's level—Innate inferiority is just how it is.
When the most basic stats are two or three times yours, no matter how perfectly you replicate it, you can't surpass the original creator.
But a gap is a gap; what does it matter?
The enemy Kiyokawa Izumi had to face wasn't Lord Madara or Kaguya from another world, but merely the upper rank five Gyokko before him.
As his breathing rhythm changed, he could clearly sense the differences between his own Breathing Technique and the Seven-Day Breathing Method; the explosive breathing used in Soundless Three Stage was the closest.
But the method of use was too crude and violent.
It involved ignoring one's own limits and performing segmented excessive breathing at the cost of damaging the body.
The Seven-Day Breathing Method is actually similar; it involves inhaling large amounts of oxygen to activate the cells throughout the body.
It can even increase lung capacity to four times the normal amount, which is terrifying.
Assuming the base lung capacity is that of an ordinary person, in a four-fold state, endurance would significantly increase, allowing for long periods of high-intensity exercise and delaying fatigue.
Immunity would be enhanced, recovery speed increased, and muscle soreness time reduced.
With more oxygen supplied to the brain, cognitive function and focus would both improve.
Such an assumption is still based on the stats of an ordinary person; if the initial stats were three or four times that of an ordinary person, it would only be more exaggerated.
The boost Kiyokawa Izumi received at this moment far exceeded his previous explosive state—having never awakened the Demon Slayer Mark, he didn't know what that felt like.
But presumably, it shouldn't be much different, right?