Part 5 — Limits of the Human Body
Daigo's voice rose once more, cutting through the room.
"This is Tier 1. These six stages—sensing, absorbing, refining, refining into Seiryu, flowing, and temporary storage—are your foundation. Every lesson, every session, every observation now matters. Ignore this, and you will fall behind before you even reach Tier 2."
The students sat in a tense silence. The weight of Daigo's words pressed down on them, and even the ones who had whispered earlier now stared forward, absorbing every term.
Haruto exhaled slowly, eyes briefly closing as he absorbed the gravity of it all. The energy around him—the faint, invisible Ryuki—was there, subtle but real. It reminded him of the morning, his determination, and the quiet training he had done alone.
This was just the beginning. And he was ready.
Daigo turned back to the board.
He raised the chalk and began to draw a human figure seated on the floor—legs crossed, back straight, hands resting on the knees. He took his time, making the posture precise.
Then he added the hands again, palms open.
"This is the Tier 1 posture," Daigo said. "And this—" he tapped the figure once, firmly, "—is the limit of your body."
He wrote above the diagram:
A shinobi cannot directly accept raw Ryuki.
A ripple passed through the room.
"That is why refinement exists," Daigo continued. "Raw Ryuki is unstable. If it enters the body directly, your system rejects it. At best, nothing happens. At worst—" he paused, "—you injure yourself."
He moved the chalk to the fingers and drew thin arrows entering the palms.
"At Tier 1, Ryuki enters only through the fingers. The palms act as buffers."
He underlined the palms.
"You do not pull the energy in. You allow it to gather."
Misaki leaned forward slightly. "So refining means changing it?"
Daigo shook his head.
"No. Refinement at Tier 1 does not alter Ryuki."
He drew a rough, uneven line entering the palm—then erased part of it, letting fragments drift outward.
"It simply means letting in only what your body can accept. The unstable parts are released back into the environment."
He redrew the line, smoother now.
"When Ryuki is accepted properly," he said, "it becomes Seiryu."
He wrote the word beside the diagram.
Then Daigo extended the chalk lines from the palms into the arms, branching naturally throughout the body—not straight channels, but organic paths.
"Seiryu does not stay in one place," he continued. "It must flow."
He tapped the branching network.
"Your body already has pathways for this flow—similar to the nervous system. You do not create them. You follow them."
He pressed the chalk hard at one point along an arm path.
"When the flow stops, and you force it—"
The chalk snapped.
"—the body takes damage."
The room went dead silent.
Daigo erased the broken point and redrew the line curving gently around it.
"If the flow stops," he said calmly, "you do not push. You adjust your breathing. Your posture. Your awareness. You let the energy find another route."
He stepped back from the board.
"This is Ryukoka—the flowing process."
Kaito's tapping had stopped completely.
Ayame's eyes stayed locked on the diagram.
Haruto sat very still, the explanation settling deep. He hadn't known the rules—but his body remembered them.
Daigo placed the chalk down.
"Tier 1 is not about power," he said. "It is about control."
The board stood filled with lines and rules that would decide who advanced—and who broke.
The silence didn't break immediately.
Then—quietly—whispers began to ripple through the room.
"So it can hurt you if you mess up…"
"Those pathways—are they the same for everyone?"
"Sounds like surgery, not fighting…"
Daigo let it happen for a few seconds. Then he turned.
"Questions," he said. "Now."
Hands rose—hesitant at first, then more confident.
Arashi Homura frowned. "Sensei, if refinement just filters Ryuki… can someone refine more than others?"
"Yes," Daigo replied immediately. "That difference is what separates average shinobi from exceptional ones."
Yuna Sekiguchi tilted her head. "If the flow stops naturally… does that mean the body rejects some paths?"
"Correct. Forcing flow ignores those warnings. That's how injuries happen."
Misaki crossed her arms. "So Tier 1 isn't weak. It's just restricted."
Daigo nodded once. "Exactly."
Then—
A single hand rose near the window.
Haruto.
The room noticed.
Daigo's gaze settled on him. "Speak."
Haruto hesitated just a fraction—then asked, steady and clear,
"Sensei… can Seiryu be used to heal?"
A murmur swept the class.
Daigo didn't look surprised. "Yes," he said. "Refined energy is used in medical fields. Accelerating recovery. Stabilizing wounds. Supporting surgical procedures."
Haruto nodded slowly, then continued, quieter but firm.
"I don't mean wounds," he said. "I mean… if an organ is lost. If a hand is cut off—can it be regenerated?"
The room went completely still.
Even Daigo paused this time.
"No," he said at last. "Not through standard methods."
Haruto's fingers tightened slightly on the desk.
"It can assist surgical reconstruction," Daigo continued, "but full regeneration of a lost body part is not something easily accomplished."
Haruto swallowed. "Not… at all?"
Daigo exhaled once.
"There are exceptions," he said. "Very few."
Several students leaned forward.
"The First Enkage," Daigo said, "and Lord Tsunami Aragi."
Haruto's head snapped up.
"…Grandma?"
Daigo met his eyes. "Yes. Lord Tsunami Aragi is one of the greatest shinobi in recorded history."
A few students exchanged shocked glances.
"She possessed a rare control over Seiryu," Daigo went on. "Beyond Tier systems. Beyond academy limits."
Hope flickered in Haruto's chest.
"And," Daigo added carefully, "there may be two or three individuals across high-ranked clans with partial regenerative ability."
Haruto's breath caught.
"But—" Daigo said.
That single word crushed the rise.
"Regeneration is unstable," he continued. "Success is rare. Failure is common."
Haruto's gaze dropped.
"…What do you mean by success?" he asked quietly.
Daigo's voice lowered.
"Lord Tsunami tried to save many lives," he said. "Especially her younger brother."
The name wasn't spoken—but it didn't need to be.
"She attempted regeneration multiple times," Daigo said. "And as I said—rarity does not guarantee success."
The room stayed silent.
"She did not succeed," Daigo finished.
Haruto stared at the desk.
Hope didn't vanish.
But it dimmed.
A few more students asked questions—about limits, about dangers, about how long Tier 1 lasted. Daigo answered each cleanly, precisely, until the curiosity settled.
Then he clapped his hands once.
"That's enough."
Chairs shifted. Spines straightened.
"Books closed," Daigo said. "You've listened long enough."
He turned toward the door.
"Now," he added, "we go to the training ground."