After waking up, when Shirou collected his memories, there was this extra information in his head...
Breathing Styles.
Breathing Styles are swordsmanship styles that makes use of an esoteric breathing technique known as Total Concentration Breathing, and are practiced and taught to be used in combat.
Breathing styles and 16 of them in total. The main breathing style is Sun breathing, and the other 15 styles were derived from it.
(Yeah, I added Light Breathing and Forest Breathing which I've seen in some fan fiction. It will make the set complete. You can already guess who will practice them.)
All known Breathing Styles currently taught are derived from Sun Breathing, the first one ever created. The majority of known Breathing Styles mimic a certain element of nature and replicates it with the user's movements, techniques and abilities.
The weapon attacks of users who use Breathing Styles are also longer ranged, possibly due to shockwaves or air pressure generated from their weapon itself when swinging and striking.
New Breathing Styles are always being created to suit user's combat needs, which results in new weapons being utilized in hunting. Such Breathing Styles embody a bigger variety of concepts, like animals, plants and emotions.
In any case, these new creations always branch out of the five fundamental Breathing Styles. Many of them are personal creations limited to only one user due to a trait or combat style unique to them, but there are cases when branching Breathing Styles have found usage from other users aside from their creators. In both cases, the users are Master-level Swordsman or at least highly-skilled and competent.
When utilizing a Breathing Style, users automatically visualize themselves manipulating the concept behind their style, making it seem as if they were using magic, though those that are less apt and proficient in their style will visualize less of it than one who is.
It's possible to blend different Breathing Styles when mastering a single one proves challenging.
Instead of giving up, swordsmen opted to modify Sun Breathing and created several "inferior" versions each of which focused on a swordsmen's individual strengths and weaknesses.
Thus, Sun Breathing spawned its first offspring; an incredibly versatile and flexible style evolved into Water Breathing; a style centered on powerful singular strikes that 'burn' evolved into Flame Breathing; a style which channeled strength into the legs to reach blinding speeds evolved into Thunder Breathing; a purely offensive style featuring swift rotational movements evolved into Wind Breathing; a style utilizing the ground to perform forceful offenses and sturdy defenses evolved into Stone Breathing.
As the years lapsed, the five fundamental Breathing Styles became passed down from generation to generation.
In their place, swordsmen created new Breathing Styles that branched from the five fundamental ones to suit their combat needs. Some were relegated to history as they lacked practitioners aside from their creator, while others survived through their learnability and non-uniqueness. Long-lived examples are Flower Breathing and Mist Breathing.
In later Era there was an influx of unique Breathing Styles. Insect Breathing and Serpent Breathing spawned from Water Breathing, Flame Breathing brought forth Love Breathing, Sound Breathing emerged from Thunder Breathing, and Beast Breathing branched from Wind Breathing. The last pair's connection is rather odd, since the role of Wind Breathing was remarkably absent during the development of Beast Breathing.
It can't be said that breathing Styles were not entirely lost to history after the chaotic era ended because Shirou is the proof of the continuation of this techniques.
If one say which is the most powerful, it would be undoubtedly sun breathing but this style is incredibly hard to master, so the other breathing styles were created by individuals who failed to master the original sun breathing.
Though they are little weaker compared to sun breathing, but no less formidable than sun breathing.
Most crucial of all, it can be mastered by ordinary people, granting them enough power to battle the monsters without relying on gods grace.
Shirou don't know where it come from but his speculation is that it's the memories of this body.
During his free time, Shirou have tested out breathing styles, and surprisingly he is compatible with Sun Breathing! and decided to practice Sun breathing with sword later.
'It's mid-afternoon now. Shirou had only just finished his prep work in kitchen, and he managed to convince Ryuu to lend her Alf's Lumina a traditional Japanese wooden training sword, to him untill he buy one later. Enough rambling, now it's time for practice...'
Sun Breathing - First Form: Dance.
The Bokken swings down, in an arching vertical slash.
Sun Breathing - Second Form: Clear Blue Sky.
A seamless transition into a horizontal 360 slash.
Sun Breathing - Third Form: Raging Sun.
Like a perfect dance, Shorou moved flinging two consecutive arching slashes around himself right after.
Shirou will have to say, the craftsmanship of this bokken is pretty good and in his preferred style, too. A Dai-Katana, more often known as an Odachi, is a Japanese great sword. His preferred length is about that of a bustar sword.
Sun Breathing - Fourth Form: Burning Bones, Summer Sun.
Shirou step forward, unleashing a singular slash with a spiraling motion. Perfect.
Though Shirou felt the sword's length isn't standard for Sun Breathing, it works just as fine. It feels much more natural this way, regardless.
Sun Breathing - Fifth Form: Setting Sun Transformation.
With a backflip, Shirou kicking off the ground with the forward momentum of his last slash, only to perform another horizontal slash, his blade creasing through the air with ease.
Sun Breathing - Sixth Form: Solar Heat Haze.
Shirou landed, and dash forward in a burst of speed, delivering a strike with his bokken at speeds that would boggle the senses.
Sun Breathing - Seventh Form: Beneficent Radiance.
Like clockwork, Shirou leaped in the air again, performing a spiraling upwards slash at some imaginary foe.
But this knowledge of how to perform the Sun Breathing isn't all Shirou got. He have practiced various martial arts through his life. He may have lost the body but the knowledge is still with him. It will be easy to train his way back to before.
Sun Breathing - Eighth Form: Sunflower Thrust.
When Shirou landed, he lashed out with the tip of his blade. Even as he could feel the force of his landing, the way the air shifts from the movements he make, the leaf atop his forehead doesn't fall off.
Shirou have a Mana, or to be exact patna pathway system and Parna with which to fill it. It was the proof him able to materialize the key at the prison dungeon earlier.
Shirou honestly couldn't say how much he actually have since he don't have anyone to compare to, but pooling his physical and mental energies is giving him what he could consider a good amount.
Sun Breathing - Ninth Form: Sun Halo Dragon Head Dance.
With a bit more strain, Shirou burst forwards into a whirlwind of movement, slashing at multiple imaginary foes with multiple full power swings.
Sun Breathing - Tenth Form: Fire Wheel.
At his last imaginary foe, rather than slash them, he jumped over them and then slash them in twine with a singular vertical slash with a circular motion.
As for everything else? Well, Shirou have got knowledge of several Japanese weapons in his head, though he have a preference for an odachi as already stated.
He also have knowledge of two Martial Arts styles; Sendo and the Water Stream Rock Smashing Fist. With these techniques, he have blitz through battles.
Sun Breathing - Eleventh Form: Fake Rainbow.
Shirou landed and immediately spiral into a burst of motion. Twisting, turning, rotating his body every which way. He blurred across the grass and see the afterimages left in his way.
Jeez. The name on that last one though. Isn't it kind of overcompensating for something?
Sun Breathing - Twelfth Form: Flame Dance.
Shirou screeched to a halt, his blade already raised. Two slashes spur forthwith, one after another, a vertical into a horizontal.
Shirou watch as the tree he just struck with that last attack slowly falls apart at the cross-shaped attack.
As Shirou breathe, sweet, fresh oxygen fills his body, and he can almost feel it as it ripples throughout his veins, bones, and muscles. Rejuvenating them in ways he didn't think were possible. His Parna, stabilized with each breath taken but to perform the thirteenth form, where he have to use sun breathing continuously while randomly change the first to twelfth from it's really not easy for Shirou at the moment.
But, really, Shirou didn't truly mind. He doubt his body could handle the full and true thirteenth form of Sun Breathing Technique as he is now. It will take time to fully master the technique but for now he will take whatever he can get.
Well it's already a blessing when he found he was compatible with Sun Breathing, where most people failed to master it. As for his martial arts...
Sendo, that other martial art Shirou mentioned before, also involved breathing. Through self-controlled respiration, it manifests some kind of energy called Hamon – or the Ripple, Wave Energy. Power like that of the Sun.
The Water Stream Rock Smashing Fist is more a defensive, counter-attacking based style, that also involves breathing and the flow of energy. Though his physique is unfortunately not up to par to handle diving into it yet, he can tell it'll work well with everything else.
Just as Shirou was about to continue his sword dance, a voice stills him.
"Ah, Shirou-kun~?" Anya half yawns, half calls.
Shirou turned towards the lazy cat, who just woken up form her secret nap. "Good Afternoon Anya-san. What is it?"
"What techniques are you practicing, they are so powerful." Anya wasn't joking. She could feel The power behind those slashes and thrusts, it was not infirior to a level 2 Adventurer.
"It's called Breathing Techniques. It can be learned and practiced by anyone. There are different techniques it's upto others to choose what suit them most. Mine is called Sun Breathing." Shirou didn't hide anything from Anya. He openly told her about the breathing techniques.
"Can I... Can I also learn those techniques?" Though hesitant Anya still asked. After all these kind of things are one's personal secret.
"Of course. After work, I'll write down the techniques, you can choose whichever suit you most." Shirou generiously offered Anya the Breathing techniques, she offered to have spar with him it was only natural for him to give something back.
From distance, Ryuu was looking at the them enviously. It was her who lent him her sword so why did that stupid cat get to learn from Shirou?!
"Ryuu-san you can also choose a Breathing technique for yourself." Noticing the dark aura around Ryuu, Shirou called her out and give her free rein to choose a suitable breathing technique for herself.
Shirou was greatly indebted to Ryuu who rescued him from that hell of a place, there is no way he would neglect this kind sister.