After class ended and I returned to my room, I began organizing my plans.
When I had just regressed, I was so busy simply preparing to enter Seongmu Academy that I had no room to plan what came next.
But now that I had stepped onto the first rung, I needed to organize—no, to plan—what would happen from here on out.
First, Yu Arin.
The major incident that would occur in the near future.
If possible, I would prevent Yu Arin's massacre by any means necessary.
However, if the massacre was destined to happen no matter how hard I tried—
Then before the incident occurred, I would kill Yu Arin with my own hands.
That had been the plan I made before regressing.
"…I thought that was a conclusion I reached after careful deliberation, but looking at it again, it feels pretty awful."
Before regressing, I knew nothing about Yu Arin.
Her captivating appearance, her clear voice.
Those large, doe-like eyes.
Facing all that, hesitation crept into the idea of killing her.
Killing a real person—not someone imagined—was never something you could grow accustomed to.
'Stay cold.'
I clenched both fists tightly and forced myself to calm down.
This life must never fail.
Not just for me, but for everyone in this country.
No matter what, I had to avoid the worst outcome.
"For now, I'll observe more and decide later."
Whether to save her, or kill her.
So what was necessary to do that?
Power.
Whether I chose to save Yu Arin or kill her, the strength to carry out that plan was essential.
I had been running like a madman until now, but that was still far from enough.
"Back to insane training again."
After being accepted into Seongmu Academy, I'd enjoyed a brief period of ease, but now it was time to run again.
Leisure was nothing more than a luxury for me.
'Just as the Grand Academician said, someone from the family will come soon.'
To teach me the martial arts of Cheongsin.
The One Sword Style.
As the name suggested, its principle was simple.
A straightforward and destructive method that killed the opponent with a single strike.
But the One Sword Style wouldn't work for me.
That didn't mean the martial art itself was weak.
My grandfather had earned the title of First Sword using the One Sword Style.
And with my grandfather's help, its shortcomings had been supplemented, to the point that even the disciples of the Cheongsin Academy now practiced it.
In time, it would grow beyond Cheongsin and become a martial art representing the entire kingdom.
'But it doesn't suit me.'
There were many reasons, but the most representative was my abysmal talent.
The One Sword Style was a martial art whose efficiency increased in direct proportion to strength.
The stronger the user became, the more explosive its efficiency grew.
A sword technique that rewarded honest training.
The problem was that my growth rate was noticeably slower than others.
No matter how limitless the technique's potential, that flaw made it unsuitable for me.
The enemies I had to face weren't humans, but Raksha.
That was why I couldn't rely solely on the One Sword Style.
"Looks like it's time to start."
If my foundational heart method, the Shinro Heart Method, was the culmination of future techniques, then what I was about to bring out now was a legend from the past.
In other words, a sword art that had faded into the shadows of history.
To explain this sword art, I had to turn back time.
To hundreds of years ago, when humans and Raksha were at war.
Back then, humanity was under the dominion of the Raksha.
There were many reasons for that, but the most crucial was that they were a race stronger than humans.
Generally, living beings maintain a balance of yin and yang.
There may be variations by species, but typically the ratio did not stray far from half and half.
When that balance collapsed, problems arose.
When yin energy increased, the body became cold and susceptible to all kinds of illnesses; when yang energy was excessive, the body could not endure it, causing numerous issues.
But Raksha were different.
Despite having nearly eighty percent yin energy within their bodies, they functioned normally in daily life, and this led to far more effective results in battle.
The yin and yang energy used by humans was overwhelmed, absorbed, or crushed by the Raksha's powerful yin energy.
Countless debates and studies followed, and eventually a theory spread: if Raksha fought using only yin energy, then humans should fight using only yang energy, its direct opposite.
The martial art born from that idea brought about a massive transformation in the world.
By wielding explosive yang energy, humans reached a level comparable to Raksha, and by leveraging their numerical advantage, gradually drove them back.
The tide of war quickly turned, and humanity ultimately seized control of the world.
But just as yin and yang coexist and balance each other, as dictated by the laws of nature—
The backlash from imbalance soon arrived.
Warriors who used the Falling Moon Sword Technique failed to live past forty in countless cases.
The cause was the extreme yang energy burning their internal organs, shortening their lifespan.
A martial art powerful enough to drive out Raksha, yet burdened with devastating side effects.
With no further need to fight Raksha, it naturally fell into obscurity and remained only as a symbol.
And now, I intended to take up that relic of history.
The Falling Moon Sword Technique, a martial art of extreme yang.
"There's no martial art better suited to me than this."
From the moment I dreamed of regression, I had scoured every grave and hidden archive in the world.
And when I discovered the secret manual of the Falling Moon Sword Technique, I found hope.
Driven by the single resolve to change history, I memorized every line from the first sentence to the last without missing a single character.
Even now, I could recite it from beginning to end.
It was time to put that knowledge to use.
"First, I'll have to train the Extreme Yang Divine Art."
The foundation of the Falling Moon Sword Technique was converting the yin energy inside the body into yang energy.
Only then could the increased yang energy be unleashed in a rampage.
The Extreme Yang Divine Art supported that process.
Yet when I was about to begin, hesitation crept in without my realizing it.
Knowing what the outcome would be, it felt like walking willingly toward my own death.
"How long will I be able to live?"
If people in the past only lived to around forty, then I had, at best, twenty-five years left?
Knowing how short that time was made death feel right in front of me.
"It'll be fine. I know how to eliminate the side effects."
The method was simple.
Don't store the yang energy—release it immediately.
That would naturally maintain the balance of yin and yang.
In other words, unless I was in combat, my body's balance wouldn't collapse.
During training, I would expel it right away.
That didn't mean there were no side effects, but I didn't care.
'I've already lived to 180 once.'
Even if it was a life filled with regret and remorse, it was far longer than that of ordinary people.
I had no more attachment to life.
That resolve had already been made when I chose regression.
Steeling my resolve once more, I changed clothes and headed to the training grounds.
Perhaps because winter had only recently passed, the sun was already setting even though it was only around five in the afternoon.
That was why the practical exam had been even more exhausting.
With April approaching and no longer seeing my breath in the air, at least that was a relief.
It was the perfect season for training.
When I arrived at the training grounds, I let out a small laugh.
"Of course it's empty."
Not a single soul in sight.
Today's classes had gone on nonstop for three hours.
They were probably racking their brains trying to review everything.
"Guess it'll take a while to get used to it."
Everyone except me would be groaning in agony for a while.
That was all thanks to thorough preparation.
After all, I had effectively prepared for 180 years.
In any case, since I had more time than the others, I couldn't afford to waste it.
"Let's do it here."
I took a wooden sword from a corner of the training grounds, spread out a mat, and sat down.
Because the ground was firmly paved, sitting for too long made your backside ache.
If I didn't want to suffer from hemorrhoids later, it was better to prepare in advance.
All preparations were complete.
Now it was time to begin the Extreme Yang Divine Art.
Since this was my first attempt at training something I only knew in theory, it wouldn't be as easy as the Shinro Heart Method.
'It's fine. Don't rush. Slow and steady.'
First, gather all the energy in my body into one place.
Because I had already pinpointed the flow of energy throughout my body while training the Heavenly Path Method, gathering it in the lower abdomen wasn't difficult.
The problem started here.
I had to precisely separate the yin and yang energy within my body.
'This is difficult.'
But what was ever easy?
This was the strongest martial art against Raksha.
If it were easy to learn, that would be far stranger.
Convincing myself, I focused my mind.
After about half an hour—
"Got it."
I managed to separate the yin and yang energy to some extent.
After that, it was simple.
Leave the yang energy in the lower abdomen and send only the yin energy up to the heart.
The organ in the human body that contains the most yang energy.
The heart was a place where yang energy made up ninety percent, with barely any yin.
What would happen if a large amount of yin energy flowed in all at once?
Naturally, the body would convert all that yin energy into yang to restore balance.
"Ugh…!"
My face twisted involuntarily.
It felt like my heart was protesting, asking why I was doing something so insane.
My heartbeat doubled in an instant, and it felt as though all the blood in my body was rushing backward.
Cold sweat broke out.
'Was it this hard?'
Just as I thought I might die, a refreshing sensation washed over me, as if all the pain before had been a lie.
Strength surged through my body, and fatigue vanished as if I'd taken a drug.
The reaction occurred as the energy within me shifted to seventy percent yang and thirty percent yin.
This was the foundation of the Falling Moon Sword Technique.
A state that pushed physical efficiency to the extreme at the cost of lifespan.
The longer I indulged in it, the more my body would deteriorate.
I immediately opened my eyes, stood up, and began releasing the yang energy.
Then I picked up the wooden sword I had prepared and swung it while infusing it with yang energy.
The wooden sword blazed with golden light, and I released my energy without restraint.
For about one minute.
After exhausting all the yang energy I had created, I collapsed onto the mat.
The earlier refreshment returned as discomfort.
It felt even worse than when I normally used internal energy.
"So this is the aftereffect."
The secret manual had mentioned the aftereffects as well.
Yang energy was like a drug—once you tasted it, it was hard to quit.
"I get it. I really do."
After lying there like a corpse for a while, I recovered enough to sit up.
"And that was only one minute?"
That meant the absolute amount of my internal energy was pitifully small.
"And it took half an hour just to create the yang energy."
That was an even more fatal problem.
What enemy would patiently wait half an hour while I separated and converted energy?
"Will I be able to shorten it in six months?"
I didn't know.
But there was no other option.
All I could do was continue training.
It was just then—
"Hm?"
I sensed a faint presence.
From behind the training grounds.
It seemed someone else was training.
Was there anyone besides me who would train on the very first day?
'Should I take a look?'
Before regressing, I had trained alone for more than half my life.
Because of that, training was truly boring.
No—more precisely, it felt unfair that I was the only one suffering.
I wanted to see someone else struggle.
'Grandfather trained with a smile, so it doesn't feel the same.'
Let's exclude my grandfather—he wasn't human.
With that thought, I headed toward where I sensed the energy.
At the center of the training grounds was a small pavilion where anyone could rest, making it easy to observe others training.
I climbed onto the pavilion and looked to see who it was.
And in the distance, I saw a black-haired girl.
An owner of beauty that didn't fade even at that distance.
It was Yu Arin.
Judging by how she was sitting with her eyes closed, was she training a heart method?
I didn't know which one, but the energy she was emitting was unusually intense.
Strong enough to be felt from afar.
And moreover—
'Why?'
The situation didn't look good.
Her energy was tangled.
Instead of yin and yang being in harmony, it looked like she was suppressing rampant yin energy.
That wasn't training.
It was merely circulating energy to calm it down.
Judging by how practiced she was, it didn't seem like something she'd only been doing for a day or two.
'A constitution with rampant yin energy…'
Excessive yang caused mania, but excessive yin led to depression.
'Is that the cause of the massacre?'
Depression could drive someone to extreme actions.
This alone wasn't enough to determine the cause of the massacre, but it was valuable information nonetheless.
Just then, Yu Arin, who had been circulating her energy, stood up with a tired expression.
It would be best to just let her go.
But for some reason, I felt like I shouldn't.
"Is it like that every day?"
"…!"
Yu Arin flinched in shock.
She clearly hadn't expected anyone to be watching.
I jumped down from the pavilion and approached her.
"It's the first day and you came out to train? Same here."
"Is that so?"
Yu Arin replied dryly and turned away.
Still a cold young lady.
Even so, I continued speaking to her.
"How long do you think you can keep suppressing that yin energy? One day, it'll swallow you."
Yu Arin turned her head and stared at me silently.
"Is that all you wanted to say?"
An expressionless face and an indifferent tone.
Yet her reaction subtly revealed that she agreed with my words.
"If that's all, aren't you just being a nag?"
I smiled faintly.
I couldn't just be a nag who gave unsolicited advice without offering a solution.
"How about giving that yin energy to me?"
"What?"
"Donate what you're not using. I need it."
Good for you, good for me—everyone benefits.