Warning sirens echoed throughout the *Argonaut*.
Every engineer, mechanic, and technician in Hangar One had been called to emergency stations.
The prototype Gundam stood in the center of the launch bay, surrounded by scaffolding and maintenance arms that were still attaching armor plates even as the reactor came online.
Unlike Aegis, its silhouette was unmistakably inspired by the legendary **RX-78 Gundam** of the Universal Century. Broad shoulders, a heroic chest, a traditional Gundam face, and a more refined frame gave it an appearance that was both familiar and entirely new. It was larger than Aegis, built around a next-generation reactor and a psycho-responsive frame that glowed faintly beneath its white armor.
Its backpack, however, hinted at what it would one day become.
Six unfinished fin funnel hardpoints extended from the rear, but only two prototype funnels were functional. The remaining four were little more than empty housings.
Flint stood beneath the mobile suit, reading the final diagnostics.
"...Power output stable."
An engineer shook his head.
"Stable isn't the same as safe."
"It never is."
"The synchronization software is only sixty-three percent complete."
Flint sighed.
"I know."
"The learning AI hasn't calibrated."
"I know."
"The emergency limiter doesn't even—"
"I KNOW!"
The hangar fell silent.
Flint rubbed his forehead.
"We're out of time."
---
Leon walked across the hangar wearing a newly fitted pilot suit.
Unlike his old one, this suit incorporated experimental neural feedback systems designed to communicate directly with the Gundam's psycho-responsive frame.
Rika met him halfway.
"You don't have to do this."
Leon smiled gently.
"If I don't..."
He looked toward the tactical display mounted above the hangar doors.
Another Federation cruiser disappeared from the battlefield.
"...who will?"
---
Mira approached carrying Leon's helmet.
She didn't joke this time.
She simply handed it to him.
"Come back."
Leon took the helmet.
"I'll try."
She frowned.
"No."
Her blue eyes met his.
"Promise."
Leon hesitated.
"...I promise."
---
Flint climbed onto the maintenance platform beside the cockpit.
"This machine doesn't have a name yet."
Leon looked up.
"It should."
Flint rested a hand against the white armor.
"It was designed to carry humanity's hopes beyond the Helix War."
He smiled slightly.
"So..."
He looked at Leon.
"...what do you call it?"
Leon studied the mobile suit for a long moment.
Then answered.
"**Sentinel.**"
The engineers exchanged approving glances.
Flint nodded.
"Gundam Sentinel."
The name spread quickly through the hangar.
Within moments, every technician was referring to it by name.
---
The cockpit closed.
The panoramic display came alive.
Unlike Aegis, Sentinel's operating system felt... alive.
A calm feminine voice echoed through the cockpit.
**Pilot authentication complete.**
**Welcome, Leon Ardent.**
Leon blinked.
"...Flint?"
Flint's voice came through the comms.
"I may have added a few features."
"You gave my Gundam a personality?"
"It helps with workload management."
"You made an AI."
"...Maybe."
Leon laughed despite himself.
"You're unbelievable."
---
The catapult locked into place.
Captain Rolf's voice echoed across the hangar.
"Leon..."
A pause.
"...Bring everyone home."
Leon looked toward the stars displayed on his cockpit monitor.
"I'll do everything I can."
---
"Catapult clear!"
"Launch path confirmed!"
"Reactor at one hundred percent!"
The launch officer raised a hand.
"Gundam Sentinel..."
A beat.
"Launch!"
---
The catapult hurled Sentinel into space.
White armor flashed beneath the light of the distant Sun.
For a brief moment, every Federation pilot still fighting near Jupiter saw a brilliant streak crossing the darkness.
One exhausted pilot whispered over an open channel,
"...A Gundam?"
---
Sentinel accelerated.
Its new reactor produced almost twice the output of Aegis, yet the machine remained remarkably stable.
Leon pushed the controls gently.
The Gundam responded instantly.
"So this is..."
He smiled.
"...what the next generation feels like."
---
Ahead, the Fourth Fleet was collapsing.
Only eighteen of its original forty-two warships remained operational.
The battlefield was littered with wreckage.
Mobile suits fought desperately against swarms of Ascendancy drones.
Leon arrived just as an Adele squadron was about to be overwhelmed.
Three drones surrounded the formation.
The pilots had nowhere left to run.
---
A beam flashed.
One drone exploded.
Before the others could react—
Sentinel crashed between them.
Its beam saber ignited in a brilliant blue arc.
One clean swing.
Two drones were cut apart.
The surviving Federation pilots stared in disbelief.
"What machine is that?"
---
Leon opened a fleet-wide channel.
"This is Lieutenant Leon Ardent."
"All surviving units..."
He looked at the tactical map.
"...fall back behind me."
The pilots hesitated.
Then obeyed.
---
The Ascendancy drones changed formation.
Rather than attacking immediately, they spread into a perfect circle around Sentinel.
Watching.
Analyzing.
The same behavior Helix had once shown.
Leon frowned.
"They're studying me."
The Gundam's AI answered.
**Confirmed. Threat evaluation in progress.**
---
Then...
One drone moved forward.
Not to attack.
To communicate.
Its voice carried across every open channel.
**"New variable detected."**
**"Designation... Sentinel."**
Leon raised an eyebrow.
"So you can talk."
**"Correction."**
**"We observe."**
Without warning—
Every drone attacked simultaneously.
---
The battle erupted.
Sentinel moved with astonishing speed.
Its psycho-frame responded almost before Leon finished thinking.
Beam saber.
Beam rifle.
Vulcans.
Shield.
Every movement flowed together.
The drones adapted quickly, but Leon adapted faster.
Within minutes, twelve drones had been destroyed.
No Federation pilot had ever achieved anything close to that.
---
Watching from the flagship of the Ascendancy fleet, a tall figure stood before a vast crystalline window.
Unlike the drones, this being was humanoid.
Its silver-white armor appeared grown rather than manufactured, etched with flowing geometric patterns that shimmered with pale blue light. A long mantle of metallic fibers drifted behind it as if underwater, and its face was hidden behind a smooth, expressionless mask with two luminous violet eyes.
It watched Sentinel in silence.
Finally, it spoke.
"Interesting."
Another figure approached.
"The Helix predictions were accurate?"
The first nodded once.
"The adaptive subject has exceeded projected development."
It turned away from the window.
"Prepare a Harbinger."
The second figure hesitated.
"Against a single mobile suit?"
The masked being looked back toward the battlefield.
"That..."
Its glowing eyes narrowed slightly.
"...is no ordinary mobile suit."
---
Near Jupiter, Flit's AGE Gundam finally arrived alongside the *Diva*'s escort force.
Leon glanced across the battlefield as the familiar blue-and-white Gundam joined the fight.
Flit's calm voice came over the private channel.
"You launched an unfinished prototype."
Leon smiled.
"You noticed."
"I noticed the missing armor."
"It'll be finished later."
"If there is a later."
Leon chuckled.
"That's why you're here."
For the first time in weeks, the two Gundams flew side by side once more.
Ahead of them, the Ascendancy fleet finally made its next move.
One of the six remaining colossal ships began to unfold.
Its central hangar slowly opened.
From the darkness within...
Something enormous stepped into the light.
The drones immediately withdrew.
Even the giant battleship gave way.
Leon felt a chill run down his spine.
"Flit..."
"I see it."
The unknown machine was nearly twice the height of a normal mobile suit.
Its body was clad in gleaming silver armor with lines of violet energy pulsing beneath the surface. Six wing-like crystalline structures floated behind it, untethered, shifting through impossible angles around its back.
It raised one hand.
The surrounding space distorted.
Then it spoke.
"I am **Harbinger One**."
"I have come to evaluate Humanity's champions."
The real battle...
Was about to begin.