[Third person Perspective]
In the mornings, Hiroto would get up and get prepared for the training to come. Tanjiro keeps a journal that he's writing in. When Hiroto asks Tanjiro why he's writing it Tanjiro responds,
"Well, I'm keeping a journal about our training and everyday life, so that when Nezuko wakes up she can read about what we did so far," Tanjiro responds by putting down the ink brush and closing his book.
Leaning sideways on the doorframe, Hiroto looks towards Nezuko's sleeping figure inside their room. Ever since the night at the temple, Nezuko hasn't woken up yet. Hiroto and Tanjiro just assume that it's probably something that Demons do to rest.
"Let's go." An aged voice comes from the main room. Tanjiro and Hiroto leave their room and close the door, taking a last look at Nezuko's sleeping figure.
When the three arrived at the clearing with the sun cascading through the forest top, Urokodaki turns and tells them. "The Demon Slayer Corps has around several hundred members." Hiroto and Tanjiro listen closely to the lecture.
"It's an organization unrecognized by the government. However, they still exist and continue to kill Demons. Nobody knows who is leading the band of Demon Hunters… still shrouded in mystery." Turning towards the rising sun, Urokodaki continues.
"Demons. Their main source of food; Humans. They kill Humans and consume their flesh. When they were first born or where they came from is still unknown. They have powerful physical abilities and even when injured, they are able to immediately heal themselves. Body parts hacked off will still have some sort of connection and they are able to grow completely new arms and legs." Pausing for a bit, he looks at the reaction of the two siblings to see them in shock at the information told of Demons.
"There also exist Demons that have incredible abilities to change their body structure. If one does not use a blade of special quality, even after chopping the Demon's head off, the Demon will not die." Urokodaki continues, as Hiroto interrupts at this point.
"Was the sword that Tomioka-san used made of the special material?" Hiroto asked, looking for confirmation.
Nodding his head Urokodaki replies, "Yes, each member of the Demon Slayer Corps carries a blade of the special material that is able to kill a Demon permanently when beheading them."
Urokodaki continues from where Hiroto interrupted him. "The Demon Slayer Corps fights the Demons with their mortal flesh and blood. Due to them being Humans their injuries recover slowly and lost limbs will never regrow. Even so, they still fight the Demons of Humanity… to protect other humans." Urokodaki concludes.
"I am a trainer! I train swordsmen. There are a lot more of these trainers who train swordsmen with a variety of techniques in a variety of places. If one wants to enter the Demon Slayer Corps then they must survive in the "Final Selection" held on Mt. Fujikasane. Whether or not you're eligible for "Final Selection"... is up to me."
*gulp* Hiroto and Tanjiro look on to Urokodaki with some anxiety.
[Training Montage (little time skips here and there)]
The two boys keep training each day, waking up early running up the mountain and passing the traps one by one again. As the days go by, the traps get deadlier and more viscous.
'He's really trying to kill us!' Hiroto thought to himself, pulling Tanjiro who is balancing himself from falling into a pit trap full of sharp blades.
*whoosh* a log flies towards their direction, forcing the two to keep running and dodging.
'We have to train our hardest so we won't die during the Final Selection. I won't be able to be with Tanjiro all the time during it, so he needs to get stronger. So do I. For Nezuko's sake.' Hiroto thought to himself.
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After repeatedly descending the mountain, day after day, the two boys start to memorize and learn how to avoid most of the traps based on instinct alone.
The constant running and jumping helps to build up their strength faster, with the two being more proficient at using their senses better than before.
With Hiroto's eyesight being more redefined, and Tanjiro's sense of smell being sharper.
However, as the two boys get stronger, the traps keep on getting more and more difficult.
Ending each day, Hiroto sits next to Nezuko as he slowly wipes her face clean from some of the dust, and Tanjiro next to his desk as always writing in his Journal. After several months had passed, the amount of books has started to increase in size as the days of training pass by.
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After half a year has passed by, the two boys were given a katana as they ran down the mountain together, dodging the traps with a sword in hand.
What they realized was that with the addition of the sword, both of their movements were hampered significantly as they had to be aware of the katana's size and how to properly hold it when running down the mountain avoiding the traps.
With the addition of the katana's, the two boys find themselves getting ensnared by traps they would've previously avoided a lot more frequently, as Tanjiro currently dangles from a foot trap upside under a tree and Hiroto being tangled up in some rope, unable to move.
In the evenings when the two descended the mountain, they would swing their katana over and over again until their swords nearly fall off.
"998! 999! 1000!!" The two boys yell out, as they swing their sword in rhythm for the final time.
"500 more!" The devil's voi *cough* Urokodaki's voice sounds out from behind, causing the two to freeze and wallow in their misfortune.
Once night arrived, as usual, Hiroto would tend to Nezuko, as well as practice how to breathe in a pattern, while Tanjiro writes in his journal of what they did during the day. When Tanjiro asked what Hiroto was doing, Hiroto responded with,
"... Breathing!"
This caused a small vein to bulge on Tanjiro's head, annoyed at the stupid simple answer, twitching.
Some days, instead of running down the mountain Urokodaki would take the two and instruct them on how to use the katana.
"Katanas break easily," Urokodaki told them.
"Though it's strong vertically, it's weak horizontally, so you need to apply the force straight along the blade," Urokodaki says, before swinging his katana at the 3 tatami mats rolled and stacked side by side. As his sword passes through effortlessly, a clean and straight diagonal line is shown from the cut made.
"The blade's direction and the direction in which you apply the force must be exactly the same." He says, before pointing towards the two boys.
"If you ever damage the blade, in other words, break it, I'll snap your bones, as well." in a threatening tone of voice. Hiroto looks away as Tanjiro's pupils into a dot.
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After some time, standing in a clearing surrounded by trees Hiroto and Tanjiro both have their sword poised ready in front of them. Opposite to them 20ft away stood Urokodaki, barehanded.
The two boys stared at Urokodaki's tengu mask not masking a move when suddenly the world started turning in front of them.
"Ehh?/Huh?" The two mutter, as they start falling to the ground sideways.
Urokodaki's body flickers away from their sight as he stands over them in a fighting pose after flipping the two on the ground.
This training session was to get the two boys used to being thrown around and recovering from any fallen position quickly while trying to defend themselves.
This continued for hours before the two collapsed from fatigue with bruises littering their bodies, and muck in their hair.
The day after, Urokodaki started teaching breathing techniques to the two boys.
When he saw Hiroto performing the proper, although slightly different, breathing form he was surprised.
"Where did you learn to do this?" Urokodaki asked him.
"Hiroto scratched the back of his head before replying, "Well, I remember my Dad telling me how to people are able to get more strength and focus better when breathing in a certain manner and pattern while I was a kid."
Tanjiro hearing this was shocked, "Dad told you that? How come I didn't know?"
"Well, you were still really young and was still crawling around so you wouldn't remember," Hiroto replied.
Urokodaki, when he heard this was curious about what their parents were but left it at that.
"This breathing technique is called "Total Concentration Breathing", and it's similar to what you did Hiroto. Did you feel your physical and mental abilities being improved when performing it?" Urokodaki said, looking towards Hiroto.
"Yes, I felt that I could move and think faster, it also enhanced my sight a lot more so I can see things easier," Hiroto said, nodding his head.
"That's right, you need to take a long breath so the oxygen flows into every cell in your body. Doing this will enhance your body's natural healing power too, and both stabilize and energize your spirit." Urokodai lectured, crossing his arms.
"What you can do Hiroto is just the tip of the iceberg. You are just starting to break through into the full extent of "Total Concentration Breathing". Relax your upper body, while bracing your lower half." Urokodaki instructed.
The two boys followed the instructions and did as told, relaxing their upper half while bracing the lower half of their bodies.
"Alright, now breathe!" Urokodaki commanded.
Tanjiro took a deep breath in*suuuuu* and exhaled *haaaaaaaa* *SMACK* "GACK!"* Tanjiro coughed out at the end of exhaling as his stomach was slapped by Urokodaki.
"Wrong!"
Hiroto on the side tried it as well, *Suuuuuuu* exhaling through his teeth, *Fooooo* as the sound of compressed air escapes from between.
"Good," Urokodaki said nodding, before slapping Hiroto's stomach too.
"GACK! What did I do wrong?!" Hiroto exclaims, clutching his stomach in pain.
"Whenever Tanjiro gets it wrong from now on, you will also be punished," Urokodaki said, in a low and menacing tone.
Hiroto slowly looked over to Tanjiro who then looked away and started whistling.
After training on breathing techniques, they were taken to a lake with a waterfall. Standing up on a cliff ledge over the water Urokodaki instructed the two boys to, "Become one with the water."
Needless to say, the two boys have never swum before so they don't know how to.
"Get in there!" Urokodaki's voice sounds out from behind as he proceeded to kick Tanjiro off the ledge.
"AGGGHhhhhhh" Tanjiro yells out as his voice fades away before *Splash* falling into the water.
"Tanjiro!" Hiroto yells before kneeling and clasping his palms together. "Don't worry Tanjiro, your big bro will look after Nezuko. Rest well in the afterlife."
Urokodaki then proceeded to kick Hiroto over the ledge as Hiroto screams out, "NEZUKOOOOooo" *splash*
Two bodies could be seen lifelessly floating in the river.
Afterward, they would have to train by withstanding the water pressure directly underneath a waterfall.
"AHH NEZUKO!! WE ARE WATER!! AHHhhhouwwwahhhh." The two voices of the boys could be heard fading under the waterfall.
Before shortly collapsing under the strong currents and floating away peacefully.