"Reiatsu is a fairly broad term. If we were to break it down… you could describe it as the density of a soul."
"The stronger the individual, the denser and heavier their soul becomes. When it's restrained, it won't show on the surface—but once it erupts, it creates a presence like a black hole."
"Yes. Like pressure—like gravity. If the gap is absurdly large, just standing nearby can make you feel like you're suffocating."
"Collapsing on the spot, being unable to stand—those are common. And if someone is physically weak, it's not impossible for it to cause shock or dizziness."
"It's a rather bullying tactic, really. In essence, it's like an adult refusing to fight a child, trying to make them back down through intimidation alone."
"Hm? You're asking if what I did to you yesterday was that?"
"Heh… Shizuya-kun, you already have your answer, don't you…?"
Now changed back into his standard black uniform, Aizen wore the same gentle smile as ever.
Facing Shizuya's suspicious stare, he pushed up his glasses, a teasing lilt in his voice.
"As I just said—using Reiatsu to bully someone is an adult picking on a child. But if the other party possesses a body no less resilient than an adult's…"
"Then the effect is reversed."
"Yes. In that case, what was meant as intimidation becomes provocation."
"Even someone utterly unaware will erupt at the most critical moment. After all, when it's life and death, you can't afford even a sliver of retreat."
At that point, Aizen's intent could not have been clearer.
Leaning back against the headboard, his expression faintly weary, Shizuya couldn't help but say, "So yesterday, you used your Reiatsu to forcefully pressure me, so I'd explode with power through sheer survival instinct?"
"Mhm. Quick to grasp it, aren't you."
Shizuya hurriedly shook his head.
"No, no, no. That method is way too weird…"
Do you really have to crush someone to the limit? I'm begging you—steady, gradual progress is the right path!
What kind of Spartan training is this…?
Shizuya wailed internally.
Doraemon Aizen—your teaching philosophy might be a little… off!
"Aha. From the results, I'll admit it deviated quite a bit from what I expected."
Aizen seemed about to cross his arms, but his brow pinched with discomfort. In the end, he let them fall.
"Destroying half the sword hall was… an accident, certainly. But I have some savings, so you needn't worry about the cost, Shizuya-kun."
"Sensei, that's not what I meant…"
It was just property. Even if he had to work for it, Shizuya was confident he could pay it back eventually.
The real issue was Aizen.
Shizuya lifted his gaze. There was guilt in his eyes.
He might be the one lying in a hospital bed, but Aizen Sōsuke was the one more grievously wounded.
That slash hadn't held back in the slightest—an explosive strike born from pure desperation.
It wasn't exaggeration to say Shizuya's "counter" had been meant to kill.
And yet Aizen hadn't defended at all. He'd simply let the attack land.
Flesh split cleanly. Bone nearly visible.
Namu San… how brutal—brutal enough that even the emergency responders who arrived had teared up on the spot.
Perhaps sensing Shizuya's gaze, Aizen kept smiling and raised a hand, pointing lightly at his chest.
"Does it bother you? This wound?"
Isn't it obvious…?
His very first time drawing steel hadn't been to cut down a Hollow, or some villain.
It had been his teacher—someone who'd helped him again and again.
Just thinking about it made his scalp prickle.
To hide his awkwardness, Shizuya scratched at the corner of his mouth.
"You don't need to blame yourself so much, Shizuya-kun. As I told you before… I, Aizen Sōsuke, am also new to being a teacher. Many things are still new to me."
"Even if I appear mature, in the end, I'm still a novice."
"How to guide students—how to help you find your own paths and draw out what people call 'potential'—that is what I must consider."
"This method… yes, in hindsight it was a rather rash attempt. But fortunately, I'm reasonably satisfied with the outcome."
So.
Aizen tilted his head slightly, lifting a hand to gesture at the bandage visible near his collarbone.
"Consider it a lesson carved into the bone. Heh. I'm sure it will be unforgettable."
It sounded nice—but it didn't ease Shizuya's guilt at all.
He wanted to say more, but with Aizen wearing that smile that didn't quite reach his eyes, Shizuya finally let out a soft sigh.
Words were useless.
Before this man fully found his "path," he really did have the makings of a… pleasure-seeking sadist, didn't he?
"Um, Sensei…"
Choosing his words carefully, Shizuya lowered his eyes.
"Thank you for the guidance."
Aizen's lips pressed together almost imperceptibly. This time he didn't answer—only turned his gaze toward the window.
"Small talk ends here, Shizuya-kun. After last night's bout, you should understand how Reiatsu functions now, yes?"
Of course.
There was no method more unforgettable than that.
Seeing Shizuya nod, Aizen gave a satisfied nod in return.
"As expected of my student. That is the level you should reach."
"Controlling one's Reiatsu with precision is a required lesson for any Shinigami—foundational among foundations. Without it, you cannot wield Kidō flexibly."
"It's like a general who can't command his own soldiers. Letting them act however they please and hunt for opportunities on their own may be one approach… but it wastes resources, doesn't it?"
Shizuya understood the theory completely.
After all, Kurosaki Ichigo in the canon timeline was exactly that kind of case—his reishi pathways were rough and unstable, the complete opposite of Unohana Retsu's smooth, well-formed passage.
"Arima-kun. Reiatsu can be trained, but in truth, everyone is born different."
"Some are tall. Some are short. Some are heavy. Some are thin."
"It's like physical ability—genes inherited at birth can impose limits on development and growth."
"But training later in life can still bring corresponding change. Up to here, Shizuya-kun, you're following, yes?"
Yes—this was the sort of thing even a sixth-grader could understand.
But what did it have to do with what they were talking about?
Perhaps sensing Shizuya's confusion, Aizen smiled at him. Something bright—something unreadable—glimmered in his eyes.
"You may not have noticed yourself, Shizuya-kun, but your Reiatsu is excessive—absurdly so."
Huh?
Is that true?
I… had no idea!
Seeing Shizuya's baffled expression, Aizen wore a look that said as expected.
"Just as I thought. The person in question has no sense of it."
"Because you haven't yet studied this systematically."
"If you wait until second year, there will be control exercises specifically for Reiatsu. At that time, you'll notice your own talent."
Then why not wait until then?!
Shizuya wailed internally… why are you in such a hurry to "develop" me?!
"Even I think taking it step by step is better. But once I saw such a deep foundation… it was difficult not to be tempted."
"I believed that with proper control, I could keep the damage to a minimum. But your Reiatsu exceeded my expectations by far…"
Aizen's gaze took on a thoughtful cast. As if to aid his thinking, his right hand rose beside his face, his index finger tapping lightly at his temple.
"Ah, yes. At this level, your power is already beyond that of ordinary unseated officers. Shizuya-kun—purely in Reiatsu, you can rival the lowest seated ranks."
Was that… good news?
Learning that he was "gifted" didn't necessarily mean much—if anything, it might simply be because he'd lived two lives.
Maybe memory could be converted into something like Reiatsu. Maybe his past experiences gave him a natural edge.
Still, he shouldn't be that far above normal—
No. Wait.
A possibility surfaced.
His ability couldn't directly raise Reiatsu in any obvious way.
But if he kept increasing his four core attributes… could that indirectly strengthen his soul?
And as a result, make his Reiatsu larger—more monstrous?
It did seem possible.
Last night's "losses" had been severe, but in terms of results—
It had all been good.
It was… satisfying, in a way.
"Looks like you gained quite a bit from this as well, Shizuya-kun."
"Uh… heh. Just a little."
Teacher and student exchanged a smile.
Not long after, Aizen left first—busy with work.
Shizuya, for his part, had only been exhausted. After a brief recovery, he went to handle his discharge.
A full day and night of sleep…
So squeezing Reiatsu to the brink and draining the body also wore out the mind.
If he had a choice, he'd rather not do something that dangerous again.
He found his sword by the bedside and hung the Asauchi at his waist. Just as he stepped off the bed—
Before he could take two steps—
The door swung open.
It was Tōsen Kaname, carrying a fruit basket. Facing Shizuya, he reflexively turned his head slightly to the side.
A brief silence.
Then he spoke softly.
"…Was I being presumptuous?"
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