The tower had spent the entire duration of his absence feeding itself…

It hadn't just passively siphoned ambient mana from the atmosphere. It had actively devoured the mutant creatures that blindly charged the perimeter, processing their corrupted flesh and cores with the exact, passive, carnivorous hunger Ren had deliberately woven into its architecture.

It was massive now, and also terrifyingly thick.

The wooden roots that Ren vaguely remembered leaving as medium-sized structural anchors had engorged themselves. They had thickened into massive, iron-hard trunks that burrowed deep into the blood-soaked earth.

The entire structure radiated a heavy, predatory presence that it absolutely hadn't possessed at this level the day Ren built it. It looked less like a guard tower and more like a massive, hungry beast waiting in the dirt.

The moment Ren reported for duty, command immediately pinned a merit badge to his chest.

Because that single tower, operating entirely alone, without a human operator, without a single drop of extra mana than his initial investment, had been systematically slaughtering the mutants approaching their sector for days.

When the Wall's logistics officers finally ran the kill-count mathematics, the final number was impossible to ignore.

The autonomous structure had reduced the total volume of creatures successfully reaching their sector of the Wall by around half.

Half.

And it had done it while Ren wasn't even there…

Even when Ren desperately tried to hide in the shadows and keep his head down, his sheer existence inevitably proved far too useful for the world to ignore.

The bureaucratic result was official, and it arrived swiftly. Ren was immediately promoted to the first true rank of military leadership on the Wall. He didn't get it for an act of suicidal bravery in frontline combat, nor did he get it for tenure. He got it because he had almost single-handedly deployed (and secretly also engineered) a self-sustaining, autonomous meat-grinder that successfully defended the kingdom 'while he slept'.

Sergeant Vehn signed the promotion paperwork with the exact same relaxed face he applied to everything else. But as he handed the signed document over, the veteran officer leveled a long, heavy stare at Ren. It was a gaze that lingered exactly one second too long. It was the calculating look of a man silently archiving a puzzle piece that didn't quite fit the narrative of only "a fairly dense management class".

Ren accepted the promotion with a perfectly neutral, unreadable mask. He didn't want a single ounce of extra attention.

But internally, his mind was racing.

'The tower works, we need to make many more…'

It didn't just work; it functioned better than his calculations had predicted. And if a single, isolated tower could execute that level of automated slaughter in a relatively quiet sector of the Wall, the defense implications were staggering.

What would happen if he deployed dozens of them? Hundreds? If he placed them in the most violently contested "red zones". allowing them to feed and grow exponentially without risking a single human life?

Especially now that his newly acquired crystal-molding techniques would make forging the needed base runes exponentially easier and vastly more flexible.

It was another massive, world-altering door opening right in front of him.

But that was a project for tomorrow. Right now, he was officially a Section Sergeant. He had a shift to cover.

And standing down the line at position seventeen, Garret was already glaring at him. The grizzled guard held a worn cup in his hand, rattling the dice loudly. He wore the exact, impatient expression of a man who had a pending bet to settle and a rematch to collect.

♢♢♢♢

Ren's absolute biggest problem upon returning to the front lines wasn't defending the Great Wall.

It was finding a place to practice…

The three-way beast fusion was absolutely not a spell a Tamer could casually rehearse in the cramped privacy of their barracks. A monstrous, mutated Hydra boasting the catastrophic footprint of a Diamond-tier entity, and Platinum size, radiating a violent, suffocating aura that rivaled or even eclipsed the legendary beasts of Dragarion… simply did not fit inside a standard defensive sector.

It certainly didn't fit in the tiny, claustrophobic stone alcove where Ren slept.

The exact microsecond he summoned the beast, the sheer concussive displacement of its mass would violently collapse a big chunk of the Wall. And if he tried to sneak out into the nearby Red Plains to practice in the dirt, his meticulously crafted "Red Pathfinder" alias would instantly disintegrate.

He would transition from being the mildly eccentric, highly competent logistics sergeant to being exposed as "Ren, the ultimate VIP of humanity", becoming the most frantically discussed subject on the entire Wall in a matter of minutes.

He desperately needed space... And he needed that space to be located miles away from the veterans he was supposedly trying to win over anonymously.

Fortunately, the military bureaucracy had just handed him a perfectly legitimate, air-tight excuse to disappear for hours at a time.

Command had formally pinned a merit badge to his chest for his profound "understanding" of the new defensive methods, specifically citing his autonomous tower installations and archery training. The damage, figuratively speaking, was already done by getting a medal. Every single commanding officer on the perimeter knew that Ren built the meat-grinder towers.

So, what better alibi could he possibly ask for than simply continuing to build them?

And it wasn't a fake excuse... Ren was going to be genuinely installing more of the autonomous structures. He was meticulously plotting them at prudent intervals, steadily extending the lethal perimeter from his home sector into increasingly distant, dangerous red zones.

The official paperwork justified itself. He had started in the heaviest, bloodiest sectors. He had empirically proven that the autonomous towers functioned flawlessly and absolutely did not misfire on allied troops.

Now that the experimental project had yielded undeniably positive, measurable kill-counts, 'official word' had come down from 'high command': there would be a massive influx of logistical investment to rapidly expand this new grid.

Installing more towers wasn't just a believable cover story; it was, quite literally, his brand-new (secretly self-assigned) full-time job.

Consequently, Ren vanished into distant wall sections for hours every single day.