Multiversal Friendship System

When Souta and the others arrived in the Demon Slayer world, they were greeted by an unusually strange scene.

Pitch black.

They couldn't see their hands in front of their faces—no light, no visibility at all.

Logically, they should have been transported directly into the wooden cabin where Nezuko was staying. Even if it was nighttime, between moonlight and lamps, it shouldn't be this dark.

Just as Souta was wondering what was going on, he noticed a flicker of light beside him.

Rin Tohsaka had taken out a gem, its magical radiance forming a makeshift light source.

Rin: "What the heck is this?"

She looked around in confusion, then turned to Souta.

Souta shook his head: "I don't know either. Let me check."

With divine assistance, his vision pierced through the darkness, stretching hundreds of meters—revealing a bright blue sky outside.

Souta: "It's daytime out there. This darkness... must be Athena's doing."

He looked at the gem in Rin's hand and said:

Souta: "As a goddess of darkness, Athena can repel light. Look at your gem."

Rin glanced at her palm—and saw the gem's glow rapidly dimming. Its magical energy was being drained fast.

Altair frowned: "Don't tell me... that goddess is up to something shady?"

The sound of blades slicing through air echoed—her 48 swords had been summoned, ready for anything.

Souta: "Let's just ask her directly."

His golden eyes flashed as he raised his hand and drew a sweeping arc in the air.

A blaze erupted from the arc, forming into a massive fireball midair.

It hovered, radiating light and heat, illuminating their surroundings.

This wasn't really for visibility—Souta just wanted to make some noise to draw Athena's attention.

But surprisingly, the first one to respond wasn't Athena—it was Nezuko.

Nezuko: "Divine One!"

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A girl in a kimono came running over from the left, followed by Tanjiro and Urokodaki, still wearing his tengu mask.

Souta: "You guys okay?"

Nezuko smiled in relief: "We're fine."

Souta gestured at the darkness: "What happened here?"

Nezuko: "It was the little girl you brought. She said she needed to expand the Underworld's authority to recall souls—then she vanished. After that, everything went black."

Souta: "Expanding Underworld authority... to summon souls, huh?"

That eased his mind.

If Athena wasn't causing trouble, then no worries. If she could handle the soul-recall part, it'd save him a lot of divine energy.

Souta: "Don't worry, everyone. It should clear up soon."

Just as he finished speaking, a voice filled with stern, divine authority boomed from above.

It wasn't heard so much as felt—directly into the brain, like an echo of spiritual force:

Athena's Voice: "By the true name of Athena, I command: Descend, O Night. Banish the sun's blessings. Open the gates to the Underworld."

Souta immediately understood—Athena was unleashing her divine essence.

She was summoning darkness—summoning the Underworld.

Athena: "Stars above, winds of night, show me the ancient dusk."

Her divine speech completed—Underworld authority activated.

The massive fireball in the sky vanished instantly, devoured by darkness.

Souta focused his senses and felt the darkness enveloping Mt. Sagiri expanding.

Once it reached its limit, the darkness began to fade—becoming translucent.

As if merging with the world itself.

Eventually, it vanished completely, and sunlight returned to the forest.

The warm light melted the tension on everyone's faces.

Souta sensed a faint tremor in the air beside him.

He turned—and there she was.

The silver-haired girl in the cat-eared knit hat floated in midair before him.

Athena.

Apparently, the goddess didn't like being looked down on—her feet rarely touched the ground, always floating to maintain eye level.

Souta: "What did you just do?"

Athena: "I linked the Underworld I govern to this world."

She took out her system phone and glanced at it, clearly impressed.

Athena: "This system is incredible. Its ability to merge different worldviews lets me connect with the Underworld even in foreign realms. With it, summoning souls will be much easier."

Souta chuckled: "Looks like you came prepared. The Underworld goddess is more reliable than I thought."

Athena: "It's a group mission, after all. Everyone plays a role."

She clearly enjoyed the praise—especially coming from a fellow god.

Among Heretic gods, it was rare to hear one praise another. They were all pretty self-centered.

Unless it came from the heart, they wouldn't bother saying such things.

So hearing Souta, a fellow divine, speak that way clearly lifted her spirits.

Of course, Athena didn't realize this was just Souta being his usual smooth-talking self.

Athena: "I'll handle the souls. But—how do you plan to resurrect the bodies?"

Souta: "I'll rewind time on their original bodies to restore them. Once the bodies are back, the souls will naturally return. I've got that part covered."

He turned to Nezuko and Tanjiro:

Souta: "Your family... they were buried, right?"

Tanjiro nodded: "Yes. Two years ago."

Souta: "Cremated?"

Tanjiro: "Yeah. Why?"

Souta (serious): "You'll need to dig up their urns."

Tanjiro froze, stunned: "...Why?"

Souta: "I need the ashes to reverse time and regenerate their bodies. You know what time reversal is, right? Basically, I'm restoring the object."

He didn't know if creating a new body from scratch would allow the soul to return.

So he wanted to play it safe and prepare both options.

He patted Tanjiro's shoulder.

Souta: "Think about it. We're talking resurrection here—digging up ashes is a small price."

Tanjiro looked conflicted, but didn't argue.

Yeah... if they could come back, what did etiquette or tradition matter?

Souta (glancing at Altair): "Altair, you handle the digging."

He'd already decided this before arriving.

Altair was basically a grave-digging pro—she'd even dug up her own mother's grave. Everyone else's? Piece of cake.

Altair: "Huh? Me? Why?"

To be honest, she wasn't thrilled about grave-digging at all.

Souta: "Out of all of us, you're the only one with experience. You'll do it faster than anyone."

Altair: "..."

She looked at her summoned swords floating nearby.

And felt a sudden, deep weariness.

She never expected Souta would slap such a label on her.

Her proud weapons... weren't made for digging graves.