"Thank you," said Shira.
"Are… are you talking to me?" asked Sakura, turning away from the spectator stands to face her interlocutor.
Shira was the eponymous leader of Team Shira— her opponents in the match that was just about to begin. He was a tall, musclebound bloke with steely grey hair and two duelling scars: one on his left cheek, and another one across his neck. He had two kunoichi for teammates: Sen, a tall, blonde kunoichi who wore her afro swept up into a ponytail, and Yome, a tiny girl with rosy cheeks, twintails, and large, owl-like eyes.
"Yes," said Shira curtly, swallowing his distaste for the woman before him as he offered a slight bow. "Lord Gaara told me it was because of you that he changed his violent ways, and for that, I am grateful."
"Is that so," said Sakura disinterestedly.
Shira's expression darkened ever so slightly.
Curious about the woman who had had such an impact on the Kazekage, Shira had followed Sakura's matches closely and taken special care to collect as much information on her as he could from his comrades in the Hidden Sand, but her general attitude was disappointing him.
It was obvious that the large-chested girl standing before him didn't take him or his teammates seriously, and that she didn't seem particularly interested in fighting them either. Even now, she'd barely given him a second glance when he'd spoken to her. Was she looking down on him because she had learned that he could only use Taijutsu, he wondered?
If so, then he would teach her the true meaning of martial arts…
"Who will you send out to fight first?" asked Baki, eyeing the two teams in turn. "Though, do keep in mind that under tournament rules, neither Akimichi Chōji nor Sen may lead, as they've already done so in the previous match."
"I'll go," said Sakura rather grumpily. "The sooner we get this over with, the better."
"I'll fight," said Shira, maintaining a neutral expression.
Unfortunately for Shira, he'd caught Sakura at a rather bad time. Under normal circumstances, she was nice and even-tempered, but when she was cross, she could be thoroughly unpleasant. Over the past two years and a half, she'd mostly adjusted to the wild mood swings that came with her newly awakened Uchiha bloodline, but her powerful emotions still had a habit of getting away from her from time to time.
Uchiha blood was just like a certain Super Soldier Serum from American comic books— it amplified both the good and the bad.
For example, upon finding themselves in an Uchiha clan member's body, a Chinese time-traveller might become even more bloodthirsty and avaricious for benefits, a Western reincarnator might become even cringier than they initially were, and a Japanese transmigrator might become even more of a degenerate gooner!
(I'm generalising, of course— there exist reasonable Chinese protagonists, charismatic Western characters that don't make you feel like groaning out loud, and NNN-following Japanese MCs that don't go around purchasing busty slaves for their harem.)
Baki, Chōji, Ino, Sen, and Yome retreated to a safe distance, leaving Sakura and Shira in the centre of the arena. Shira took up a fighting stance, but Sakura maintained a sort of Fool's guard— that is, she remained planted right there on the spot, with her arms hanging casually at her sides.
"BEGIN!" shouted Baki.
Shira immediately lowered his gaze, careful not to meet Sakura's eyes. According to the information he'd gathered from his comrades, she possessed a two-tomoe Sharingan. Her Dōjutsu might have pretty much gone extinct from the Shinobi World, but the Sand's war archives still held records of the Uchiha, and they all said the same thing: to look an Uchiha in the eye was as good as signing your own death warrant.
For some reason, his opponent Uchiha Sakura hadn't used her Genjutsu so far in the third exam— perhaps she favoured using flashier Ninjutsu to impress the judges for a better shot at a promotion, or perhaps she was simply looking down on her opponents— but either way, Shira had no intention of underestimating her.
Shira took in a deep breath, filling his lungs with air. He was going all out from the start!
"Seven Heavens Breathing Method: First Activation!"
…
It must be known that human lungs are an extremely inefficient organ.
When a person takes a breath, stale air mixes with fresh air, diluting the oxygen concentration in the lungs before it can even reach the bloodstream— and as if that weren't inefficient enough, the concentration gradient at the exchange point is utterly dreadful as well.
At the blood-air barrier, the lungs' alveoli perform gaseous exchanges with the capillaries via passive diffusion (CO2 comes out of the blood and O2 goes in), because nature abhors a vacuum. O2 will move from areas of high concentration (the alveoli) to areas of low concentration (used blood) … but the problem is that between breaths, the air just sits there in the alveoli, while the blood flows in a set direction, which means that O2 levels at the two exchange points will naturally attain an equilibrium at 50%/50%... at best. At this point, there is no more concentration gradient.
That's a 50% loss, when you could be breathing half as much for the same result! Such a waste of effort!
However, by using his Seven Heavens Breathing Method, Shira could achieve near perfect efficiency in the gaseous exchanges taking place in his lungs. By using chakra to force the air in his lungs to move in a fixed, one-way flow, he ensured that there was always a concentration gradient— that is, there was never a moment in which oxygen-rich air couldn't find low-oxygen blood to perform an exchange with. What's more, he could ensure that old, stale air could remain separate from new, fresh air, further increasing his efficiency!
Unfortunately, there is such a thing as too much of a good thing: namely, oxygen toxicity.
As the name suggests, oxidation, a destructive process in which electrons are lost, is pretty much oxygen's fault (most of the time, since it's the most common oxidising agent). Oxygen might be necessary for us to live, but too much of it can kill…
Flames and rusting metal are but two very visual examples of oxidation, but it can also happen to one's tissues: causing cellular damage that can lead to cancer (which is why antioxidant is such a popular buzzword in yogurt advertisements).
To avoid hyperoxia (whose symptoms include: breathing difficulties; chest pain; light-headedness; disorientation; cell collapse in the lungs, nervous system, and eyes; seizures, retinal detachment, death, etc.), Shira has no choice but to metabolise his oxygen as quickly as possible by overclocking his bodily processes… which inevitably causes tissue damage as well. Even so, the payoff is worth the price: The Seven Heavens Breathing Method also grants power equal to the release of the Eight Inner Gates!