The vibrating system phone snapped Souta back to reality.
Suppressing the lingering "heat" in his chest, he opened the chat interface and saw a message from Nezuko.
Nezuko: "@Souta. God-sama, where did you all go? You disappeared so suddenly."
Souta felt a little amused. Isn't that a bit slow of a reaction?
They'd been gone for quite a while now.
Still, despite the urge to tease, he didn't say anything blunt.
Souta: "The mission was complete, so we each returned to our own worlds."
Nezuko: "You went back?"
Nezuko: "I was so caught up in the joy of reuniting with my family, I didn't even get to thank you properly. I'm really, really sorry."
Souta: "No need to be so formal. You're with your family again—of course you need time together. You can thank us anytime, no rush."
Altair: "@Nezuko. I agree. Don't worry too much. We each got what we needed out of the mission. If you want to thank us, there'll be plenty of chances during future meetups."
Kurumi Tokisaki: "Souta, your mission's done?"
Souta: "Yup, I'm back in my world now."
Souta: "Kurumi, how's your Sephira Crystal advancement going?"
Kurumi: "It's only been an hour here, but my reiryoku has already quintupled. It's growing steadily."
Altair: "Five times already?!"
Kurumi: "Actually, that's pretty slow. I've been suppressing my absorption speed to avoid accidents. Only after the Sephiral Crystal's level rose did I start to ease that limit."
Souta: "Have you awakened a new 'Angel'? Or rather... a 'Demon King'?"
Kurumi: "Hmm? Why do you ask?"
Souta: "You know how Mio originally created the Sephiral Crystals in their reversed state, right? When implanted into humans, they'd over-erode the body and cause berserking. She'd then kill the resulting Spirit to refine the Core. After multiple refinements, the Core would stabilize, allowing the human to become a stable Spirit. You're aware of that?"
Kurumi: "Yes, I am. Are you saying awakening new powers is related?"
Souta: "Exactly. It means the Spirits' powers are inherently incomplete—because the Cores were weakened through refinement. Their reversed forms are stronger, which proves this."
Souta: "Your Sephiral Crystal is evolving—likely returning to its original state and power. So I suspect you'll eventually awaken your Reversed self's 'Demon King.' Your reversed form could manipulate space, after all."
Altair: "Wait—won't that be dangerous? The original Cores corrode human bodies, right?"
Souta: "Relax. I already used a ton of divine power when I installed the 'Spirit Formula' into her. Kurumi's body and Crystal are now completely fused—like one entity. There's no more erosion risk. I mean, how could you corrode yourself?"
Altair: "Then it's fine. I'm curious—have you awakened a new power, Kurumi?"
Kurumi: "I haven't gained a new 'Angel' or 'Demon King' yet. But... my shadow space has mutated."
Souta: "What kind of mutation?"
Kurumi: "It seems like my shadow can now devour space, causing damage similar to a spacequake."
Souta: "Wait—that's 'Demon King: Lucifugus: Leo Bullet Arie,' isn't it?"
Kurumi: "Leo Bullet Arie?"
Souta: "Yeah. It's one of your reversed form's 'Demon King' bullets. It chases enemies based on your will, leaves behind a white trail, and rips apart space on impact—basically weaponized spacequake energy."
Souta: "If your shadow space is showing those effects, then it might be the prototype of your reversed self's 'Demon King.' Keep upgrading your Crystal and it might return to full form."
At this moment, Souta finally understood why Kurumi had powers beyond her Angel.
Other Spirits could only use their Angels.
But Kurumi also had her shadow-space ability beyond Zafkiel.
He'd always wondered—why did she get an extra cheat?
Now that the Sephiral Crystal's evolution was affecting her shadow, the answer made sense.
If her Crystal originally included space-manipulating Demon King abilities, and the shadow space was a degraded version of that power, it all checked out.
Though just a theory, Souta felt it was likely true.
Kurumi: "A~ra, doesn't that mean you can comfortably live off women now, Souta?"
Rin Tohsaka: "Scumbag."
Souta suddenly didn't want to talk anymore.
We were having a perfectly serious discussion—why'd it suddenly turn into teasing again?
His back almost gave out from the whiplash.
Fortunately, Nezuko came in with a save.
Nezuko: "God-sama, I've been informed of your talk with Master Urokodaki. He said he'll go to the Demon Slayer HQ in two days to report everything."
Souta: "Tell him it's fine to spend more time with his students. There's no rush on my end."
Souta: "Also, Nezuko, have your family stay in Mount Sagiri for now. Don't go anywhere. Once the Corps leader hears about me, he'll arrange official identities for your family. Until then, don't go out—it'll just cause unnecessary trouble if people find out."
Nezuko: "Understood. I'll make sure of it."
Nezuko: "Also... God-sama, can I use my points to request your help in becoming stronger?"
Souta blinked at the message.
Nezuko? Wanting to get stronger?
Didn't she want to live peacefully with her revived family?
Souta: "Sure, but what's your goal?"
Souta: "You're not planning to defeat Muzan Kibutsuji, are you?"
Nezuko: "God-sama, so you already knew?"
Nezuko: "Yes. No matter what, I can't forgive that man."
Souta fell into thought.
Nezuko seeking revenge didn't surprise him—that's why he hadn't gone after Muzan himself.
In the Demon Slayer world, paths to power were few: turning into a demon, mastering Breathing Techniques, reaching Transparent World, awakening Marks...
None seemed especially scalable.
He wasn't sure how to boost Nezuko's strength in a meaningful, original way.
Just dumping divine power to enhance her physically felt crude and wasteful.
Wait... doesn't her Blood Demon Art suppress other demons' abilities?
Suddenly, Souta had an idea.