Sun Slayer's radiance

“So is anypony going to tell me why he wanted us to meet here?” A tired and grumpy Rainbow dash complained.

Though it was early morning, the still present gray clouds blocked most of the sun's light. Last night, Yoriichi had sent a letter to all five of them saying to meet up at the open field next to the Everfree forest. Being on short notice, the mares, except applejack, were tired and ragged at getting up so early with Rarity complaining the most.

“If that stallion doesn’t have a good reason for ruining my beauty sleep, he’s going to wish he would have stayed in bed!” The furious fashionista yelled. Just then, two figures in the distance walked toward the group, soon becoming recognized as Yoriichi and Fluttershy.

Applejack sighed and rolled her eyes, “Quiet yer complain’ Rarity, they’re here.” She pointed a hoof at the pair as they both stopped.

“I apologize for making you all get up so early, but it is of the utmost importance.” Yoriichi reached his head over and grabbed a long felt bag from Fluttershy’s back and placed it on the ground. When he opened it up, the tired mares became confused when the contents of the bag were six wooden swords.

“Ooooh! I didn’t know we were playing with a pinata!” Pinkie happily cheered.

Yoriichi held back a confused look and shook his head, “Now is not the time for festivities, Pinkie. I ask of you all to take one.” He ordered.

The group didn’t question it, and; one by one, each mare took a wooden sword and stepped back. Twilight and Rarity held theirs in their magic, Applejack and Rainbow dash awkwardly tried to straighten them in their mouths, And Pinkie pie was balancing her on top of her head. Once the group got situated, Twilight chose to speak up.

“Now what?” She asked confusingly.

Her question didn’t receive an answer as Yoriichi bent down, bit into the last sword handle, and raised his head back up. He then raised his head high into the sky and, with a grunt, brought the wooden weapons down with mighty strength. The force of Yorrichi swing cracked the wooden sword, and when it was an inch from the ground, shattered into hundreds of splinters. All the mares yelped in surprise and jumped back from the blast of wood shrapnel. Yoriichi then spat the broken handle of the sword on the ground and faced the mares.

The group was silent until Rainbow dash flew upwards with a mid-air spin, seemingly wide awake now. “That was so cool!” She shouted excitedly. Rainbow flew up to Yoriichi with a starry-eyed look. “How did you do that, you have to teach me!” The prismatic pegasus practically begged.

“You’re in luck then.” Yoriichi simply said, allowing a small grin to show. “Because you all are going to need to learn that and more.” He said in a serious tone. Rainbow raised an eyebrow before Applejack bit onto her tail and dragged her back, scolding her quietly on manners. “To put it simply, Celestia and I have theorized that Muzan is planning something, maybe even a war.”

That statement caused the group to go silent and stare at Yoriichi with shock. “WHAT!?” Twilight shouted. “What’s this about a war? Who is this Muzan pony?” She demanded, accidentally dropping her sword to the ground.

Yorrichi looked down and narrowed his eyes, “It is just a theory, but we can’t take the chance of a war breaking out, because the demons would slaughter countless innocents in no time.” The group grimaced at the possibility, are demons strong enough to wipe out that many ponies? “As for Muzan. To put it simply, he is the one creating demons. The man is ruthless and uncaring, a being that even I am weary of." When Yoriichi had said that last part, the mares couldn't help but feel their hearts drop. "So we need all the help we can get.”

If they had to be honest, the thought of them going against this Muzan pony was terrifying. They had gone against threats like Nightmare moon, Discord, Chrysalis; heck, even Tirek for Celestia's sake! But they always used the Elements for those kinds of situations. This time, they had to fight a villain that would see to their deaths without hesitation, and not feel bad about it afterward. In addition, he had Starlight convert into the same monsters that attacked Canterlot, making her stronger than the first time they met. The mares' fears were visible by their expressions and trembling bodies, and it hadn't gone unnoticed by Yoriichi.

“I understand if you all aren’t comfortable with the idea. But my brother and I, despite our strength, cannot go against Muzan and his demons alone.” Yoriichi lifted his head and looked at the mare with hardened eyes.

“So I ask of you, leave me to take you all in as my students and train you in the art of Breathing techniques.”

Most of the mares looked at each other in confusion, all but Twilight, who gasped in joy. Her fear and confusion disappeared from her body in an instant as she pushed past her friends. “Wait! Do you mean the thing you use to fight demons? THAT breathing technique?” When Yoriichi nodded, Twilight squealed happily and gave a little dance of joy.

“Yes, I will be teaching you the basics of Breathing techniques so that you may grow stronger.” With the strange assistance of Pinkie pie, a chalkboard appeared behind the stallion, much to his confusion. “To learn this art, you need to practice three things: breathing control, strength and stamina endurance, spatial awareness, and style mastery. Everything else you will learn along the way. Today, we will begin breathing exercises and how to increase air intake and control.”

“That’s good an’ all, but what bout’ Fluttershy?” Applejack said, pointing her hoof at the shy mare.

Fluttershy smiled and waved her farm friend off. “I tried, but I don’t think I’m ready for his training yet, it sounds intense.” She said with a shudder.

Before Applejack could ask what she’d meant, Yoriichi spoke up. “Yes. And by the end of your training, I expect every one of you to do as I did.” With that, he began instructing them all to swing their swords in order to use them effectively. Little did the five know, the next few months of their lives would be absolute Tartarus.

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Month 1

When Yoriichi said that they would all be taking a trip to a high mountain in deep Equestria, the expectation was to go to a fancy or well-kept hotel or resort for training. Although it was mostly Rarity that thought that. But they were surprised and disappointed to find out it was the complete opposite.

The mountain itself was higher than the one they ran the dragon out of many years ago. It was high enough to the point that the air was barely breathable; it was so thin. The forest surrounding the mountain was almost or just as dark as the Everfree, accompanied by strange animal sounds and creepy creatures. It made it all the worst when the place they’d be sleeping in wasn’t even halfway done being built.

Apparently, Celestia had sent out a team to the mountain and set up temporary residence in the harsh environment. After unpacking, the mares didn’t even have time to settle down before Yoriichi started ordering them outside. For the first of their breathing control training, Yoriichi said to run all the way down to the bottom of the mountain, then run back up. It sounded tiring to them, but it wasn’t the end of the-

“You’ll also have to avoid traps that could knock the air out of your lungs,” Yoriichi explained.

Now a sense of dread had taken the hearts of the mares. As Yoriichi went on to explain, the mountain has traps placed in specific locations on the route down. One missed step could mean a bruise or two and what little oxygen they had escaping their lungs. This was to ensure that their reflexes would be sharpened and so they could learn something called total concentration breathing.

The only reason they didn’t complain is that they knew the importance of this training. So after getting into starting positions, they were off.

Of course, Rainbow dash was off first as she dashed through the air with a smug grin on her face. Immediately after a few seconds of flying, her lungs felt empty, and her breathing became ragged. She huffed and puffed as she tried to keep herself from passing out. Unfortunately, the pegasus was blindsided by a tied-up log impacting her in the side. The trap sent her crashing to the ground with a solid thud and knocked Rainbow out cold.

With Applejack and Rarity, the two made good progress, in the sense that they didn’t get hit already. A single trap was sprung by Rarity, sending a bent thin tree whipping at her. Luckily Applejack saw this and pushed the fashionista out the way and took the hit. Air left her lungs and Applejack felt as if she was going to suffocate to death. Rarity came over in time and helped the farm mare to her hooves, soon the two were on their way down the mountain again.

Over with Pinkie and Twilight, the studious alicorn had become adjusted to the darkness in her surroundings faster than her friends. She easily avoided traps that nearly missed her eye. The only problem was her breathing, even with her added strength and stamina of being an alicorn, the taxing feeling was slowly catching up.

Pinkie pie though seemed to intentionally activate the traps on purpose. She giggled and laughed as she effortlessly dodged every trap in her way as the party mare's tail and ears twitched.

To say it was a long night would be an understatement. By the end of the day, with the moon high in the sky, all the mares shuffled and dragged themselves back up the mountain like zombies. Their lungs and bodies were on fire, and the look in their eyes suggested death as a viable option for escaping this torture. But it was quickly cured by a warm meal prepared by the workers and Yoriichi upon their return.

And since the small home wasn’t done yet, the group had to resort to using sleeping bags for beds and sleeping out in the open. The mares couldn’t get enough sleep on the account of Rarity screaming in fear every time a bug crawled on her, or a rustling noise came from afar.

This…went on for the entire time.

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Month 2

By the end of the second month, the mares had made steady progress, especially Pinkie and Rainbow dash. Compared to the first day, they all could easily make their way down the mountain without too much trouble. Even the traps became easy to avoid and made their reaction times faster. But with all the time they spent training, the hardest part was avoiding the dangerous traps.

Yoriichi had noticed the mare’s improvement to see in coming threats, so he made a “small” increase to the route's difficulty. Instead of just trees and wire traps, real arrows and blades were thrown at the mares, forcing them to waste their breath dodging, or block them. There were injuries, but the worst one was a cut Pinkie had gotten on her flank when she got too confident. Despite the obvious life hazards, the mares learned to block the blades and avoid spike pits.

The same procedure went on like this for the rest of the week and by the weekend they had mastered total concentration and breathing with blood, sweat, and tears. As a bonus, the house was done being built during that time. So the group was feeling confident, to say the least.

Until…

“Total concentration breathing constant?” Rarity asked with her hairbrush in a blue aura.

Yoriichi nodded, “So far, you all have exceeded my expectations. Most new slayers would take weeks, even months, to master Total concentration breathing. But now that we are on the topic of breathing control, the next step is to learn Total concentration breathing constant.”

The concept was simple. Since normal total concentration breathing heightened a ponies body and mind, the constant version was that but it would require them to use the technique all the time.

The only problem was that Total consecration breathing was impossible for the mares to keep going more than a few seconds, any longer causing their eardrums to blow out and lungs to burn. So the concept wasn’t so simple after Yoriichi’s explanation.

So for the rest of the month, between their normal breathing training and constant training, the mares were barely functioning by the end of it. It didn’t help that they were also forced to do physical exercise in the thin air climate. Rarity, on the other hoof, got off easy from it since Yoriichi allowed it, leaving the others to suffer ribbed muscle fibers.

It was a brutal time with breaks few and far between. Sometimes Applejack and Rainbow dash worked hard into the night lifting large rocks or running circles around the house. But their efforts paid off by the end of the month.

Blade traps were nothing more than annoying obstacles, they ran marathons around the highest peak of the mountain, and did Total concentration breathing constant all the while. Yoriichi was surprised by the effort put in by his friends, most slayers gave up at this stage, and yet, they persisted and actually learned the technique ahead of schedule.

He couldn’t help but smile as he watched the future demon slayers train in front of him. Memories of his fellow demon slayers learning the same way came back to him. Water, stone, fire, wind, and thunder were the fundamental aspects of what made breathing techniques what they are. Sun breathing being the seed of the tree that birthed these techniques. And soon, these five would add branches to that ever-growing tree and stand up to Muzans terror.