The Land Of The Sun was a peaceful place. Sure, it was constantly cloudy and they hadn't seen the Sunshine, but it was a beautiful place to be in. The current shogun of the The Land Of The Sun was known as Ryuya Ryudo, the most well respected person in the entire country and for good reason.
Unlike in Clover, Heart, Diamond and Spade Kingdom, they didn't use Grimoires, rather scrolls with them being known as Yojutsu.
But there was a person there that felt like his Yojutsu wasn't skilled in the likes of using a scroll, but had the ability of something called Breathing where the user takes a deep breath as his senses and body sharpen to whole new level that maximes his strength to a way like no other.
The man was known was Yoriichi Tsugikuni. The younger twin brother of Michikatsu Tsugikuni, who wanted to become the strongest samurai aka a member of the Ryuzen Seven, but the dream will be tough as even Yami Ichika, a woman that could kill someone with a single backhand, is weaker than Yosuga Mushogatake.
Michikatsu looked at his brother with pity as the poor boy was almost mute, never talking until the time he got a flute from his elder brother when he was beaten by his father, but he never really hated him.
He was quite proud of his younger brother when he saw him find love. Yoriichi met Uta as the two were grown quickly to each other as he took care of her since she had no family.
But when Yoriichi wanted to help Michikatsu achieve his dream of the strongest by training, he felt a rush of power whenever he took a breath as he could basically see his brother's organs shifting every time he moved as his Breath were that of the Sun as his elder brother could barely keep up, even when trying to use his Ki.
He then realized the strength of his own. Yoriichi knew that he couldn't use this power to hurt people, but rather help them, save them from trouble and make them feel safe. Not to mention, he wanted to keep Uta safe.
The Tsugikuni family was always known for having other worldly Yojutsu as they know that their father has Star Yojutsu, their mother had Gravity Yojutsu while Michikatsu had Moon Yojutsu and Yoriichi had Sun Yojutsu.
Yoriichi was always skilled with the blade as he was like lightning as not even seasoned Zetten users like Komari Imari as he was almost always faster than them, but due to their experience and skill, they won.
Yoriichi realized that he wasn't the only one though. As he saw others being more skilled with a blade than with their own Yojutsu as he had thought. He was skilled with the blade and onto the properties into it, he could possibly make it easily to take down his foes.
Sure it took a while to master it, but when he did, he was an almost completely different beast as even someone like Ichika had troubles keeping up with him.
When Yoriichi asked the idea of adding a new type of teaching and fighting style to the Shogun, Ryuya Ryudo, Ryuya thought it was a good idea since he did look at people and saw they had an almost similar problem to Yoriichi, so he thought it would be a good way for them to learn so they can defend themselves.
Yoriichi was glad that Ryuya was understanding and after a chat and cup of tea thanks to the Ochami doll, Yoriichi left and posed the idea to his elder brother about if he could also teach along him the others of Breathing which he agreed to it.
As Yoriichi and Michikatsu taught several students the strength, importance and the usability of Breathing as they saw 5 different branches to it, Rock Breathing thanks to Gyomei Himejima, Flame Breathing thanks to Kyojuro Rengoku, Water Breathing thanks to Giyuu Tomioka, Wind Breathing thanks to Sanemi Shinazugawa and Thunder Breathing thanks to Jigora Kuwajima.
Not to mention, Yoriichi soonly after was engaged to Uta which Michikatsu was the victim of all of the sweet talk between the two and Yoriichi was basically an unoffical member of the Ryuzen Seven with the other creators of the Breath making a group that was second to them, known as the Hashira.
And that was the story of the originator of the Breaths, Yoriichi Tsugikuni, The Sun Breathing/Yojutsu User.
A/N:
So this was a bit random, I know, but this was in my mind when I read Demon Slayer (Up To Chapter 191 when publishing this.) and I had an idea of what if I added Demon Slayer elements into the Land Of The Sun, as Yoriichi was the originator of them in the series and basically being one of the strongest characters in The Land Of The Sun, but if I had to pick in which placement, I would say 3rd strongest, behind Ichika and Yosuga.
This was inspired by Apocrypha by LoneTaker about this Idea, but I wanted to dwell on this idea a lil more.
And also, I kind of plan to add this in my Black Clover Story: Star Magic: Yuno, when I get to that part.
Hope ya' enjoy it and see ya'!