Chapter 4: Alliance Under the Crimson Sky

The decision to form a temporary alliance did not bring relief. If anything, it deepened the tension hanging over the eastern forest like a storm refusing to break. The soldiers from the Eryndor Warbound stood in disciplined silence, watching Tempest’s forces with equal parts caution and calculation. On the other side, Rimuru’s allies did not lower their guard, even if no one had yet crossed blades. The rift behind them continued to pulse, growing larger in slow, unsettling rhythms, as though something far beyond it was pressing closer.

Rimuru stepped slightly forward, positioning himself between both groups—not as a shield, but as a boundary. “We start by securing the immediate area,” he said firmly. “No unnecessary fighting. We don’t know how stable this rift is.”

The Eryndor commander gave a short nod. “Agreed. But understand this—if that thing behind us breaks through, hesitation will kill everyone here.”

Shion clicked her tongue softly, gripping her weapon tighter. “I don’t like how calmly you talk about death.”

The commander glanced at her briefly. “I don’t like dying either. That’s why I’m still alive.”

Benimaru exhaled slowly, clearly restraining his irritation. “Then let’s focus on preventing that outcome.”

Without further delay, both sides began moving.

Tempest forces spread outward in defensive formation, securing the forest perimeter. The Eryndor soldiers moved in parallel, not interfering, but clearly studying every movement, every technique, every magical signature they encountered. It was not trust that guided them—it was necessity.

Rimuru remained near the rift with Benimaru and the commander, observing closely. The crack in the sky had grown into something vast now, stretching like a scar across reality. Within it, faint silhouettes of distant landscapes could be seen—mountains from another world, skies that did not belong here, and flashes of warlike destruction echoing far beyond reach.

“It’s stabilizing further,” the commander muttered. “That’s not good.”

Rimuru narrowed his eyes. “Why?”

“Because stabilization means permanent passage,” he replied. “And permanent passage means both worlds will start leaking into each other without control.”

Before Rimuru could respond, the ground beneath them trembled.

A deep, resonant roar echoed from within the rift.

Everyone froze.

Then it came through.

A massive creature emerged first—not fully, but enough to force its presence into this world. Its body was jagged and uneven, like armor formed from broken landscapes. Its limbs dragged against the air itself as it forced its way through, tearing the edges of the rift wider with each movement. The pressure it emitted alone pushed weaker soldiers back.

Shion immediately stepped forward. “That one looks fun.”

“Shion, wait,” Rimuru said sharply.

But it was too late.

The creature slammed one limb down, sending a shockwave through the forest. Trees snapped like twigs, and the ground fractured outward. Tempest soldiers scattered, while Eryndor troops formed defensive formations instantly, as if they had trained for this exact scenario countless times.

“Now!” the commander shouted. “Before it fully stabilizes in your world!”

The battle erupted.

Benimaru moved first, flames erupting around his blade as he dashed forward, striking the creature’s leg with a sweeping arc of fire. The impact scorched the surface, but instead of weakening, the creature adapted—its body shifting, reinforcing the damaged area almost instantly.

“Tch… it’s adjusting,” Benimaru muttered.

Shion followed immediately, leaping into the air and bringing her massive weapon down with brutal force. The strike landed cleanly, cracking part of the creature’s armored surface—but again, the damage began to regenerate.

Rimuru watched carefully. “It’s not just strong… it’s learning from every attack.”

The commander appeared beside him briefly, cutting through smaller fragments that spawned from the creature’s body. “That’s typical of rift-born war beasts. They adapt until something kills them fast enough that they can’t adjust.”

Rimuru turned slightly. “Then we don’t give it time.”

He stepped forward.

The air around him shifted as he concentrated. Not overwhelming power, but precision. The battlefield was chaotic, but Rimuru’s mind was calm, analyzing every movement, every regeneration pattern, every weakness forming and disappearing in seconds.

“Benimaru! Shion! Force it to expose its core structure!” he called out.

Shion grinned. “Finally, a plan I like!”

She launched herself forward again, this time targeting joints instead of mass. Benimaru coordinated instantly, directing flame strikes to guide the creature’s movements rather than damage it directly. The commander and Eryndor soldiers supported from range, using coordinated magic bursts to restrict its mobility.

Slowly, the creature was being pushed into a controlled position.

But then the rift behind it pulsed violently.

Another roar echoed.

Rimuru’s eyes widened slightly. “There’s more coming through…”

And he was right.

Smaller war beasts began spilling out behind the larger one, filling the battlefield with chaos. The alliance formation wavered for a moment as the pressure increased.

“Hold the line!” the commander shouted.

Benimaru clicked his tongue. “This is getting annoying fast.”

Rimuru made his decision.

“Everyone fall back five steps!” he ordered.

“What?” Shion shouted mid-fight. “Now?!”

“Trust me!”

Reluctantly, both sides disengaged just enough to reposition. In that brief moment, Rimuru stepped forward alone.

The air around him tightened.

Not explosively. Not violently.

But decisively.

He raised his hand toward the massive creature and focused on a single point—the distortion in its movement pattern, the unstable core where regeneration was weakest during transition.

“Got you,” he muttered.

A compressed burst of energy erupted—not a wide attack, but a focused strike that pierced directly through the creature’s shifting armor. The impact didn’t explode outward. Instead, it drilled inward, collapsing its internal structure for a brief moment.

The creature let out a distorted roar, staggering.

“Now!” Rimuru shouted.

Benimaru reacted instantly. Flames surged in a spiraling arc that engulfed the exposed weakness. Shion followed with a devastating downward strike that shattered the reinforced exterior. The commander and Eryndor forces unleashed a synchronized wave of magic, sealing the attack cycle.

The creature finally collapsed, its massive form dissolving into fragments of fading crimson light.

For a moment, silence returned.

Only the rift remained, still unstable, still dangerous.

Rimuru exhaled slowly. “That was just one…”

The commander stepped forward, watching the rift carefully. “Then you understand now. This isn’t an invasion of numbers. It’s an invasion of escalation.”

Rimuru glanced at him. “Explain.”

“Every time something crosses over,” the commander said, “the passage becomes easier. Stronger things follow. That was a mid-tier breach guardian. Which means…”

He didn’t finish the sentence.

He didn’t need to.

Rimuru already understood.

If that was not even the worst they had to face, then what lay beyond the rift was something far more dangerous than anything Tempest had encountered before.

Behind them, the crimson sky flickered again.

But this time, it did not feel like an opening.

It felt like something on the other side had finally noticed them properly.