Power Index.
In this world, it is a numerical value used to directly quantify a fighter's physical offensive strength — calculated without factoring in Haki or Devil Fruit abilities.
An ordinary adult male, even after receiving basic Marine training, typically has a Power Index of only 10.
For comparison, the infamous benchmark from Enies Lobby, CP9's chief Spandam, had a pitiful score of 9.
Within the Marines, the Power Index serves as a reference for evaluating the strength of mid- and lower-ranking personnel.
At the Marine Academy under Zephyr's leadership, Power Index testing is also part of the students' assessment criteria.
The minimum requirement for admission is 80, while graduation requires 500, with no upper limit.
Of course, the Power Index is only one of many graduation standards. Leadership, knowledge, and other abilities are also evaluated.
Before long, Zephyr led Yoriichi Tsugikuni to an open training ground.
Standing before him was a massive stone wall — a perfect 5×5×5-meter cube. Attached to its side was a small display panel currently reading 0.
Zephyr walked up and lightly tapped the wall.
"Yoriichi, this is the 'instrument' used to measure Power Index."
"The wall is made entirely of Seastone — incredibly durable. When you strike it, the force is converted and displayed as a numerical value."
"Like this."
He extended two fingers and tapped the wall as though knocking on a door.
Despite the casual motion, the enormous wall produced a heavy thud and visibly shifted back several centimeters.
Boom!
The display flickered rapidly before settling at 1213.
Zephyr nodded in satisfaction.
Ten seconds later, the wall slowly slid back to its original position, as if pulled by a hidden spring.
Yoriichi Tsugikuni watched with fascination. It was his first time seeing a device capable of directly measuring attack power.
Still, he couldn't help wondering — with something this massive, how could an ordinary person even move it? Zephyr had only pushed it back slightly, yet the value exceeded 1200. A normal person probably wouldn't register anything at all.
"Go ahead, Yoriichi. Give it your strongest attack."
Zephyr gestured toward the wall.
Curious, Yoriichi Tsugikuni stepped forward, planted his feet, and threw a full-force punch into the stone.
The wall didn't budge.
But the display beside Zephyr began flickering before stopping at 520.
"Heh, only this much?" Zephyr said aloud, though his eyes showed clear approval.
At that moment, Yoriichi Tsugikuni suddenly stepped back and drew the black blade at his waist.
He adjusted his breathing.
Flames seemed to coil around the sword, painting his face crimson.
Sun Breathing — Third Form — Raging Sun Mirror!
CLANG!!!
Unlike the dull thud of his punch, the blade striking Seastone rang out like metal colliding.
The massive wall was forced back several meters before coming to a stop.
The display surged — 5333.
Zephyr turned to look. For a split second, surprise flashed across his face, but it vanished almost immediately.
"Hm… not bad. Fairly decent."
His tone remained calm, but inside, waves of shock crashed through him.
A Power Index above 5000 — what did that mean?
Most Marine Vice Admirals, without counting Devil Fruit powers, fell between 2000 and 4000. Only the very strongest approached 5000 — excluding Garp.
Even Luffy in his Gear Second days would have barely surpassed that range.
A score above 5000 meant that, anywhere on the seas, you were far from insignificant.
And yet, this was a teenage boy Garp had casually brought back from the East Blue.
Still, Zephyr maintained his composed teacher's demeanor.
"Yoriichi, you'll need to keep training hard."
"Five thousand is nothing — you're still far from ready."
"When you can reach my level, then you'll barely be qualified to head out to sea."
As he spoke, Zephyr stepped in front of the wall again, inhaled deeply, and drove a punch into it.
BOOM!
The wall shot back over ten meters. The display jumped to 7000, then glitched into unreadable digits.
With a sharp crack, the mechanism anchoring the wall snapped, and the entire structure toppled and rolled away.
"To move this wall at all requires at least 1000."
"As for me… I'm roughly at ten thousand."
"You've still got a long way to go, kid. Train under me, and I'll make you into a proper Marine."
Yoriichi Tsugikuni stared in stunned silence.
"Come on," Zephyr said. "Let's look at the rest. Training starts tomorrow — with me personally."
He walked off without even glancing back at the smoking, broken testing device.
Not long after they left, instructors rushed over and stood speechless at the wreckage.
For the rest of the day, Yoriichi Tsugikuni followed Zephyr around the academy, listening as he introduced every facility. In the afternoon, Zephyr even took him on a tour of Marineford itself.
Along the way, they ran into many people — old comrades, former students, and officers who admired Zephyr. In high spirits, Zephyr greeted them all and introduced his new disciple.
"Oh! You're back!"
"This kid? My new student."
"Strength? Nothing special — only scored a little over five thousand on his first test."
Yoriichi Tsugikuni lost count of how many times Zephyr repeated that line.
Still, by the end of the day, he had grown familiar with Marineford.
That night, after a full day of walking, he returned home and sat in the corridor outside his room, leaning against a pillar and gazing at the sky.
"The night sky here… feels deeper than the last world."
"And the stars… shine brighter too."