Crossover: The Problematic Deity of Arcadia

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The moment Shinobu saw Ryo standing under the sunlight, her heart dropped in terror.

Sunlight kills demons—everyone in the Demon Slayer world knows that. It's a truth passed down for over a thousand years.

And yet, despite that lethal weakness, humans have constantly lost the war against demons.

But now, right before their eyes stood a demon who could walk in the sun.

And not just any demon—he might even be that demon. The Demon King himself: Muzan Kibutsuji.

That realization filled Shinobu with a deep sense of despair.

If demons no longer had their greatest weakness, they were no longer flawed creatures. They were perfect predators. And the balance in the war between humans and demons? It had just tipped drastically.

"Sis, I'll hold him off. You have to get word to the Master and the other Hashira!"

Shinobu stepped forward, placing herself in front of her sister, Kanae, fully prepared to die if that's what it took.

"...If you can, please take care of yourself. And Kanao, too."

In that instant, the atmosphere felt like a tragic farewell before death.

But just as Shinobu was bracing herself for battle, Kanae calmly placed a hand on her shoulder.

"Shinobu. Wait a second."

"Why are you still here?! Please, go!" Shinobu's voice trembled with urgency.

Kanae simply shook her head and gently patted her sister's shoulder.

"First off, there's no such thing as a demon who can walk in the sun."

"No, there is, sis. He is right—"

Before Shinobu could even finish her sentence, Kanae cut her off. "That man isn't a demon."

"Wait, what? Huh?"

Shinobu blinked, stunned by what she'd just heard.

A human?

Was her sister joking right now?

Then Kanae turned to Ryo, offering an apologetic smile.

"Mr. Demon—ah, sorry, force of habit. May I call you Mr. Ryo Yagami instead?"

Ryo chuckled at that. "Quick on the uptake, huh?"

She bowed slightly. "I'm very sorry. My sister and I mistook you for a demon."

"I can understand why." Ryo nodded slightly, signaling that he accepted her apology... but then added, "But that doesn't mean I forgive you."

Kanae looked up, a bit puzzled. "Then... what would it take for you to forgive us?"

Ryo rubbed his chin thoughtfully before flashing a mischievous grin.

"A place to stay, food, a Nichirin Blade, access to breathing techniques, and some demon materials. Get me all that, and I'll call it even."

"I understand. I can provide food and a place to stay right away. As for the rest, I'll need to check with my superiors." Kanae nodded firmly.

Considering how powerful and unpredictable Ryo was, a few supplies were a small price to pay for peace.

"Huh? Why are we the ones who have to provide all that?" Shinobu looked baffled by the whole thing.

Kanae gave her a light bop on the head and said softly, "Because you overreacted, that's why."

"Wha—?!"

Shinobu stared at her, stunned. "Is this really my fault?!"

Wait a second…

Wasn't it Kanae who snuck out first? Shinobu only followed out of concern. Then she caught her sister chatting in a random alley, calling someone "Mr. Demon."

Then Ryo showed up, casually flexed, and crushed the air with his grip. How could anyone not assume he was a demon?! A human couldn't possibly have that kind of strength!

So... whose fault was it really?

That nickname—"Mr. Demon"—that's what started it all!

Realizing this, Shinobu couldn't help but cry out: "Sis!!"

Kanae, looking completely serious, said, "Shinobu, when you make a mistake, you apologize and try to fix it. Got it?"

"..." Shinobu looked like she was about to cry.

"There, there, don't be upset. What matters is you understand now." Kanae gently patted her sister's head, then turned to Ryo.

"Mr. Ryo, would you mind stepping inside with us?"

"Sure," he replied with a nod.

— — —

Later, in the courtyard by the Butterfly Mansion …

Shinobu sat stiffly on her knees, an annoyed look on her face as she handed over freshly brewed tea and some snacks.

Ryo glanced at her, and she immediately changed her expression to something more composed and polite, giving him a small nod.

But as soon as Kanae turned away, her scowl came right back.

"Hmph," she huffed, plopping down beside him with a pout.

Kanae just stuck her tongue out playfully. "She's got a bit of a temper. Hope you can forgive her."

"No problem," Ryo said calmly, taking a sip of the tea. "It's good tea."

"Thank you for the compliment," Kanae replied with a smile.

Then, after composing herself a bit, she looked at him curiously.

"There's something I've been meaning to ask, if you don't mind?"

"Go ahead," Ryo said, picking up a tea snack.

"You're human... right?"

"I am."

Kanae hesitated, then continued, "But earlier… you crushed air with your grip. And there's also that diary of yours…"

"Does that really matter so much to you?" Ryo tilted his head slightly, eyes narrowing with quiet amusement.

"Ah…" Kanae blinked, then smiled. "No, you're right. It doesn't."

Whatever secrets Ryo had were his business. As long as he wasn't a demon, Kanae didn't care.

"Alright then," Ryo said, changing the subject. "Let's talk about something else. I read what you wrote in your diary."

Kanae immediately lit up. "You mean the question I wrote—'Can demons and humans ever get along?' That one?"

Shinobu's eye twitched at that. She stared at her sister, alarmed.

She'd heard Kanae say that before, but never in front of outsiders.

'My dear sister! Are you trying to get yourself branded a lunatic?!'

If any other Demon Slayer heard that—especially one who'd lost loved ones—they'd think Kanae had lost her mind.

Shinobu screamed internally but kept quiet with Ryo still present.

Meanwhile, Ryo's lips curled into a smirk.

"Of course humans and demons can get along," he said.

"Really?" Kanae's eyes sparkled. "How? How can I make that happen?"

Ryo's smile deepened, tinged with something dark.

He chuckled softly and said, "Easy."

"Just kill every last demon. Turn them into nothing more than folklore—myths people tell around a campfire."

"Once that happens, humans and demons can live in peace."

Kanae's expression froze.

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.

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