The dawn light filtered weakly through the dense canopy, casting pale shadows on the battered battlefield. The forest, once alive with the roaring tide of monsters, now lay quiet except for the distant chirping of unfamiliar birds.
Rael hefted the last of the beast cores and elemental crystals into the makeshift storage area of the fortress. The air still smelled of smoke and metal.
Beside him, Eren carefully examined the cores with his small device, his brow furrowed in concentration.
"So, these are the cores you said you can use?" Rael asked, watching the boy's quick fingers manipulate the holographic display.
"Yes," Eren replied, eyes flicking between the cores and his device. "Each core is like a seed of life, but with mechanical properties. You can combine them with the right components to create new creatures — mechanized beasts with specialized abilities."
Rael nodded slowly. "I've been experimenting, but I don't fully understand the limits. There has to be a better way to optimize their power."
Eren's lips curved into a small smile. "That's where my System comes in. The Research System can analyze the cores, cross-reference them with materials, and suggest the best combinations for upgrades."
Rael glanced at the boy — despite his young age, Eren's calm confidence was something rare in this brutal world.
"Well," Rael said, "Let's see what you can do."
Eren set up a small portable terminal in the fortress's command center, its interface flickering to life as he synced his device with the fortress's core network.
The holographic screen bloomed with data — layers of schematics, molecular structures, energy flow simulations, and beast core signatures.
"Your current mechanized beast, Iron Fang, was built from a combination of the Wolf Core and Titan Frame components," Eren explained. "But the core energy is underutilized. With some elemental crystal infusion, we can boost its attack power and speed significantly."
Rael leaned forward, eyes scanning the detailed report. The system even suggested a prototype design for a new type of armament, integrating plasma cannons with hydraulic claws.
"This could turn the tide in battle," Rael muttered. "But we'll need more resources."
Eren nodded. "And that's why research is only part of the battle. We have to expand, gather materials, and defend the fortress."
Days passed as Rael and Eren worked side by side. Rael hunted the wilds to gather more beast cores, elemental crystals, and rare metals, while Eren spent hours analyzing and upgrading the fortress's mechanized arsenal.
One evening, after an exhausting day of salvaging and research, the first prototype from their collaboration was ready.
Rael and Eren stood together in the main hangar as the large mechanical hatch slid open. Inside lay a sleek, quadrupedal machine, its frame slimmer but more agile than Iron Fang.
"This is the Sentinel," Eren announced. "Using a Fox Core combined with elemental crystals, it has enhanced stealth capabilities and can fire concentrated energy blasts."
Rael nodded in approval. "Let's test it."
With a command, the Sentinel whirred to life, its optics glowing faintly. It moved with fluid grace, darting around obstacles and firing precision blasts at distant targets.
Rael felt a thrill surge through him. "This is the beginning."
But the night brought no true rest. Word of the blood moon's corruption and the increased monster strength had spread through the scattered colonies of Castle Lords and other species.
Rael checked the world comms channel, messages flashing with reports of fierce attacks and dwindling supplies.
He knew the tides would come again — bigger, more dangerous, and relentless.
Beside him, Eren packed his research gear. "I'll continue refining the designs. If we can improve our defenses and mechanized troops quickly, we might just survive."
Rael clapped the boy on the shoulder. "Then we fight, we build, and we conquer. Together."
As the blood-red sky darkened once more, the fortress hummed with renewed life — a bastion not just of steel and fire, but of hope.