Demon Slayer: Seraph of Radiance

"You want to be with me forever too, right, Onii-chan?"

Sayuki's soft voice whispered into Kawanishi's ear, as delicate and sweet as dewdrops falling on young leaves. Yet beneath that tenderness was an alluring, dangerous power — like a witch's whisper, stirring something within his heart.

But Kawanishi suppressed the turmoil, calmly shaking his head.

"Why… why have you become like this?"

Sayuki gently rubbed her cheek against his neck, her voice tender.

"Because I love you so much, Onii-chan. I don't want to leave. I don't want to die."

She then gracefully pulled away and glided toward the nearby trash bin in the room.

Kawanishi watched her quietly, not interrupting her movements.

Retch—

Sayuki bent over, vomiting up the fruits and rice balls she had eaten earlier. Her face twisted in discomfort.

"What an idiot... you went out and ate again," she muttered.

Wiping the corner of her mouth, Sayuki tiptoed back to Kawanishi, locking eyes with him.

"Onii-chan, are you afraid of me now that I've become a demon?"

Kawanishi clenched his fist.

"No. Onii-chan isn't afraid of his little sister."

Sayuki suddenly giggled, her laughter crisp like silver bells.

"That's good. Because I really do want to be with you forever."

Her demonic power stirred within her. Kawanishi answered,

"I feel the same. I also want to be with Sayuki forever."

Become one with me… let your strength join mine, and we'll never be apart…

Sayuki sighed as if recalling something unpleasant, puffing out her cheeks in frustration.

"But Onii-chan, you'll age, get sick, and die… while I won't."

"How can we be together forever?"

From Kawanishi's back, black thorny vines crawled upward, their sharp spikes tearing through his ruined clothes, revealing his hardened body.

The thorns snaked around his neck, tightening.

"Of course — by eating you! If I devour you, we'll become one and never be apart!"

The black thorns suddenly constricted, aiming to strangle him.

Kawanishi's expression remained calm, his gaze fixed on Sayuki's transforming face.

"Is that enough?"

Under the moonlight, his iron body reflected a dark metallic sheen. No matter how the spikes dug in, they couldn't pierce his flesh. His fangs protruded, his veins pulsing like writhing serpents beneath his skin — Kawanishi had fully demonized.

With his transformation complete, he calmly looked down at Sayuki.

Sayuki stared at his demon form, her eyes lighting up with crazed joy, nearly squealing in delight.

In the next instant, the black thorns around his neck dissolved into blood and vanished.

Sayuki clapped her hands in glee.

"Onii-chan, you're a demon too! No wonder you wouldn't eat with that fool."

"This means… I don't have to eat you anymore. I'm so happy, so happy!"

But Kawanishi's eyes flickered with doubt.

That fool? She had said it twice now — and she was referring to herself. Odd, considering her behavior thus far seemed fully human until now.

There's something I don't know yet…

He was ready to summon his Flame Feathers, but instead, he let his blood demon art dissipate.

"Yes, Sayuki — now we can truly be together forever."

"Tell me, how did you become a demon?"

"Tell me everything that happened to you."

Upon hearing "Sayuki," her expression abruptly turned cold, her tone dark.

"Onii-chan, don't call me Sayuki anymore."

"My name is Sayuki no longer. I am Satsuki. She created me — but she's already gone."

Satsuki… Sayuki…

Countless thoughts flooded Kawanishi's mind, forming a painful yet increasingly clear picture.

Is Sayuki's true self… really gone?

If she is, I can wield my blade without hesitation. But if not… what then?

Satsuki grasped his hand with a gentle smile.

"Onii-chan, what are you thinking? From now on, call me Satsuki, okay?"

Kawanishi smiled gently — though his demonic face made that smile appear feral.

He softly stroked her hair, though it felt prickly now — nothing like the silky golden strands he once knew.

"Satsuki… does Sayuki still exist? Has she truly vanished?"

Satsuki's eyes snapped open at his words, her face turning ice cold.

Her thorn-like black hair trembled like venomous snakes.

"I said — Sayuki no longer exists."

"She died the moment she was shot."

"This body belongs solely to me — I am Satsuki!"

"Onii-chan, you're not allowed to mention her again."

Kawanishi's heart sank.

Then Sayuki… is truly gone?

Standing before him now was someone familiar yet completely foreign — no longer his sweet little sister, but a demon named Satsuki, obsessed and deranged, driven by a twisted form of love.

Satsuki caressed his hand and whispered playfully,

"By the way, did you like that haori?"

"I carefully picked out the best materials. I had to kill dozens of people to make it, you know."

Kawanishi's lips curled into a dangerous grin.

"Of course. But it's ruined now — what a shame."

He tossed the tattered haori to the ground, then slowly embraced Satsuki, pulling her close against his chest.

Satsuki giggled, snuggling into him.

"I saw it got ruined."

"But that's okay. If you want, I'll make you a new one."

"All it takes… is killing more people."

Kawanishi softly repeated,

"Yes… just killing more people…"

"They must have suffered terribly before they died."

His gaze darkened, eyes gleaming dangerously.

Satsuki paused.

"Onii-chan, what do you mean?"

Suddenly, Kawanishi's arms tightened like a vice, crushing her body with immense strength. Bones cracked beneath the pressure.

Behind him, luminous white wings of flame unfolded — the Asahi Blade.

Satsuki cried out in pain as her ribs shattered. At that moment, crystalline needles whirled within her eyes, like a rotating starlit sky.

"Blood Demon Art: Thorn Mirage — Optical Deception."

The Asahi Blade slashed forward — but Kawanishi found her form had vanished from his grasp.

The blade halted before it struck, retracting back into its winged form.

Then, Kawanishi noticed her again — directly ahead — falling backward rapidly.

The Asahi Blade resumed its arc, streaking through the air like lightning.

Splurt.

A spatter of demon blood landed on Kawanishi's face.

In an instant, Satsuki's figure vanished once more. A crash sounded above as the rooftop burst open.

Kawanishi looked up to see her hovering, gazing down from the rooftop. Blood flowed from a fresh wound on her pale arm — but it was already healing quickly.

Satsuki dipped her slender finger into her blood, licking it seductively before covering her mouth, giggling.

"Onii-chan… what are you trying to do? You've made me so sad…"

Though smiling, tears rolled down her cheeks.

(End of Chapter)