Kamado Tanjiro's Hinokami Kagura burst into full power, his orange-red blade flashing like the blazing sun at noon, slashing straight for Tomioka Giyu's face.
This strike was sharper and more refined than any before. The red glow of the fire dragon rippled along his Nichirin Sword, and the snow around them melted instantly under the searing heat.
Giyu's pupils tightened. Blood still seeped from the wound on his left arm, but his expression remained calm—
he knew this was the decisive blow, the moment of everyone's breakthrough, the final test of this training.
"Blood Demon Art: Water Vortex Barrier!"
Giyu's voice was low but forceful. Black blood flowed from his wound and fused with the surrounding melted snow, swirling together into a spinning vortex nearly two meters wide in front of him.
The whirlpool radiated freezing cold. When the fiery blade struck it, most of its power was instantly absorbed by the spinning flow. The orange glow dimmed within the rotating water.
But Tanjiro didn't stop. His Sun Breathing surged again, forcing his blade deeper into the spinning current. "Giyu-san! This time, we won't lose!"
"You've done well, Tanjiro."
A faint look of approval flashed in Giyu's eyes. While holding his sword with his right hand, he pressed his left palm firmly into the vortex's center. "But it's not enough—the core of the vortex is the key! Watch closely!"
At his touch, black blood condensed at the vortex's center. In an instant, its spin intensified, flinging Tanjiro's fiery slash backward with a burst of force.
Just then, Shinazugawa Sanemi's green storm surged in from the side. His wind blades, laced with snow and ice, cut sharply toward the weakened edge of the whirlpool. "Wind Breathing, Tenth Form: Whirling Sandstorm—Modified!"
This time, he followed Giyu's earlier lesson about using the opponent's momentum. The storm flowed with the vortex's spin, slicing through its rotation and tearing open a crack.
Tomioka Tō's pale-blue storm blades followed instantly, raining in with precision. "Storm Breathing: Modified—Breaking Wave Wind!"
He had finally mastered channeling power from his core. The strike was nearly twice as fast as before—his blades skimmed Giyu's right arm, leaving a fresh cut and scattering black droplets across the snow.
Cracks spread across Giyu's vortex barrier. He immediately shifted his blood technique. "Blood Demon Art: Frozen Spiral Vortex!"
The water froze at once, sharp icicles shooting out from the vortex walls in all directions. The shards whistled through the air, so fast they left afterimages, one narrowly missing Tanjiro's shoulder.
"Use Hinokami Kagura to melt the ice!"
Giyu's voice echoed across the battlefield.
Tanjiro obeyed immediately—his orange-red aura flared brighter, melting the incoming shards into mist before they could reach him.
Kanroji Kanae seized the moment, channeling her Flower Breathing. A soft pink aura swirled through the mist, forming a petal shield to hold back the shattered fragments and open a path for attack. "Flower Breathing, Fifth Form: Peonies of Futility!"
Uzui Tengen's golden blades of Sound Breathing followed the rhythm of his score, slicing in rapid arcs along the barrier's edge. "Sound Breathing, Seventh Form: Raging Performance!"
His blade light shimmered like vibrating strings, each strike landing precisely at Giyu's defensive openings.
Kocho Shinobu moved silently around the rear, her faint violet aura concentrating into a stinger of poison. "Insect Breathing: Dance of the Dragonfly – Compound Eye Hexagon!"
She aimed directly for Giyu's still-healing wound.
Now besieged from six directions, Giyu was forced to defend all sides. Black blood dotted the snow beneath his feet.
He thought to himself with a sigh, Butterfly really isn't holding back at all…
His Water Vortex Barrier shattered completely. Switching between Water Breathing and Blood Demon Arts, he defended purely on instinct—using "Water Breathing, Eleventh Form: Dead Calm" to deflect frontal strikes, and "Blood Demon Art: Binding Water Threads" to entangle incoming wind blades.
But even so, the wounds on his body multiplied. His deep blue uniform was nearly blackened by blood.
"Push harder! He's about to drop!"
Sanemi shouted, his storm intensifying again, the red glow of his Mark burning fiercely across his face.
Tanjiro's Sun Breathing reached its peak, his blade radiating intense heat as he charged. "Giyu-san—here I come!"
As the fiery blade closed in, Giyu didn't raise his guard. Instead, he slowly sheathed his sword.
His pale-blue aura faded, and the black demon energy receded. He stood still in the center of the snow, surrounded by their blades.
Tanjiro's Nichirin Sword stopped one inch from his throat. Sanemi's wind blade pressed against his chest. Tō's storm slash grazed his left shoulder. Shinobu's stinger poised near his waist, while Tengen and Kanae's blades locked his limbs in place.
"Stop."
Giyu's voice was calm but weary. "Training is over."
Everyone lowered their blades at once. Seeing the wounds that covered him, they looked both shocked and guilty.
Tanjiro quickly held out a salve. "Giyu-san, are you alright? Did we go too far?"
"I'm fine."
Giyu took the medicine and spread it casually over his wounds.
Black blood stopped flowing almost instantly, the skin around each cut twitching faintly as it began to close.
He's never consumed humans, Tanjiro thought, so his regeneration must be weaker.
"The healing of demons is stronger than you think," Giyu said evenly. "And only through this kind of fight can you truly grasp the power of your Marks."
He looked at everyone, faint satisfaction glinting in his dark blue eyes. "All of you have surpassed my expectations. Once we finish brewing the formula I remember—the one that removes the Mark's side effects—your strength will rise to another level."
The group nodded firmly, fire rekindled in their hearts.
They were exhausted, but their spirits burned brighter than ever.
...
Inside the stone chamber of the Infinity Castle, the candlelight flickered, casting shifting shadows across the cold walls.
Iguro Obanai leaned against the icy stone, holding a neatly folded letter in his hand. His fingertips brushed the paper gently, his eyes filled with an uncommon softness—
it was a letter riskily smuggled to him by a Kakushi, from Kanroji Mitsuri, the Love Hashira.
He carefully unfolded it. On the pale yellow paper, Mitsuri's lively, graceful handwriting danced across the page. The faint scent of sakura lingered in the ink.
"Iguro-san~ How have you been lately? I bet you're secretly training again, aren't you? Don't overwork yourself, okay? Remember to eat properly!"
Obanai's lips curved into a small smile. He could picture Mitsuri fretting over his meals, just as she always did—she'd even sneak rice balls into his hands during training.
He read on. "Yesterday I ate three bowls of salmon chazuke and Shinobu's red bean soup! It was super sweet! I wanted to save some for you, but I accidentally ate it all. Next time you're back, I'll make sure to save a bowl just for you!"
At the words "accidentally ate it all," Obanai couldn't help but let out a quiet laugh—
he knew her too well. She always meant to save something but never could resist good food.
There was even a faint red smudge where some red bean soup had stained the fold of the paper—
a small, human imperfection that made the letter feel all the more real.
"During training today, I taught the new recruits Love Breathing! They said I was amazing! But I tripped and scraped my knee a little. Shinobu-chan put medicine on it—it doesn't hurt at all, so don't worry, okay?"
Next to the sentence was a little crooked doodle of a smiling face with the note: "I'm super brave!"
Obanai ran his finger gently over the drawing, his gaze full of tenderness.
He knew that though Mitsuri acted carefree, she was actually scared of pain—but in her letters, she always pretended to be strong.
He remembered once during training, when she fell and tried not to cry, saying, "I'm fine, I can keep going!"—until he blew gently on her scraped knee, and she finally smiled again.
"Oh, and Iguro-san, when will you come back? I've been saving lots of wagashi—strawberry ones, matcha ones—all your favorites! Also, Tanjiro and the others said they're improving fast! When you're back, let's go eat three bowls of noodles together, okay?"
At the bottom, her signature was followed by a doodle of two hands linked together—
one with snake-like scales, one with a heart pattern. Their secret mark.
Obanai pressed the letter to his chest and closed his eyes. He could almost see her: sitting by the Butterfly Mansion's window, sunlight spilling over her pink hair, pen in hand, smiling to herself as she wrote—
sometimes frowning when she couldn't find the right words.
His chest felt warm, but beneath that warmth, a dull ache lingered.
He couldn't return yet. He had to stay hidden in the Infinity Castle, spying close to Kibutsuji Muzan, risking everything to feed information back to the Demon Slayer Corps.
From his robes, he pulled a rolled-up parchment—his own hand-drawn map of the Infinity Castle.
It detailed Muzan's palace, the locations of the Upper Moons, and secret passages leading toward the armory.
He had gathered this information bit by bit under the guise of routine patrols—planning to pass it on to the Kakushi during his next contact.
"Wait for me, Mitsuri," he whispered softly, his finger pausing over a red mark labeled exit.
At that moment, footsteps echoed beyond the chamber door, followed by a demon's voice.
"Yatsuki-sama, Lord Muzan summons you. He says there's something important to be discussed."
Obanai immediately folded the letter and the map. The letter he tucked inside his belt, the map he rolled thin and hid inside his boot.
Taking a steadying breath, he suppressed the tenderness in his heart, letting his expression return to its usual cold, emotionless calm.
He pushed open the door and followed the demon down the dark corridor toward Muzan's throne hall.
The black mist along the walls writhed like a living thing. Obanai's footsteps remained measured, though his mind raced—
Muzan summoning me without warning... could it be he's noticed something in the north? Or begun to suspect me?
Whatever it was, he would have to stay calm—he couldn't afford a single mistake.
At the door to the throne room, he stopped and adjusted his black haori, making sure not a single detail seemed out of place.
Then, with a quiet exhale, he stepped into the suffocating darkness.
He knew this game of deception was far from over—
and that every move he made now could determine the Corps' survival… and whether he'd ever return to Mitsuri's side.
Inside the chamber, Muzan floated midair, his crimson eyes glinting like molten metal.
"Yatsuki," Muzan's voice was cold as frost, "Hantengu is dead. Slain by the Demon Slayers. You will leave for the northern region at once. Mushiki is there. Join him and wipe them all out."
"As you command," Obanai bowed low, hiding the flicker of emotion that rose in his chest—
Hantengu's death meant Tanjiro and the others had succeeded.
He would use this mission as a chance to send word to the Corps, to let them know they were not alone.
Muzan seemed satisfied. "Go. Do not disappoint me."
Obanai turned to leave. The dark mist brushed coldly against his cheek, but it couldn't reach the warmth in his heart.
He gripped the hidden letter at his waist, his steps growing firmer with each stride.
For Mitsuri. For the Demon Slayer Corps. For a future without demons.
He would not stop until it was real.
Side Story 2 : Summer Night Festival
Evenings at the Butterfly Mansion were always steeped in the soft fragrance of wisteria.
The setting sun stretched the wooden window shadows long across the floor, falling over the medicine chest that Shinobu was carefully organizing.
She had just placed the last bottle of coagulant inside when a gentle knock came from the door.
"Coming."
Shinobu rose with a small smile, her fingertips still faintly stained with pale green ointment.
When she slid open the door, Tomioka Giyu was standing in the corridor. The deep blue of his Water Hashira uniform made his posture look even more composed, and in his hand was a plain cloth bundle. The tips of his ears carried a faint shade of red.
"Ready?"
His voice was softer than usual, his eyes landing briefly on the hem of her kimono—a light lavender one, embroidered with delicate butterfly patterns along the skirt. It was the same one Kanae had helped her choose last time.
"Of course I'm ready."
Shinobu gave her folding fan a playful wave and teased, "Giyu-san is surprisingly punctual today. I thought you'd show up half an hour early to wait."
The redness deepened on Giyu's ears as he handed her the cloth bundle. "There's mosquito repellent inside. And... Kanae-san said there'll be crowds at the festival, so she sent this hairpin for you."
Inside lay a silver butterfly hairpin. Tiny pearls glimmered softly on its wings, catching the sunset light.
When Shinobu took the bundle, her fingers brushed his by accident. Both froze for a second.
Giyu quickly withdrew his hand and looked toward the wisteria in the courtyard. "Let's go. If we're late, we'll miss the fireworks."
Shinobu stifled a laugh and followed him.
They walked side by side along the country path. The evening breeze carried the faint scent of ripening rice fields, lifting the hem of Shinobu's kimono and brushing through Giyu's dark hair.
At first, the walk was quiet. Then Shinobu suddenly stopped, pointing toward the roadside. "Look! Fireflies!"
Giyu followed her gaze—
tiny green lights flickered across the grass, like stars scattered in the night.
He said nothing, only slowed his pace a little so she could watch longer.
When she finally turned back, realizing he'd been waiting for her, her cheeks flushed. "Come on, come on, or we'll miss the fireworks."
By the time they reached the town festival, the sky had gone completely dark.
Red lanterns lined both sides of the street, steam rose from food stalls, and the air was filled with the smell of grilled fish and sweet syrup. Children ran past holding spinning pinwheels, their laughter carried by the summer wind.
Shinobu's eyes immediately caught a taiyaki stand. She tugged at Giyu's sleeve with a bright grin. "I want red bean filling!"
He followed her without protest, his steps unconsciously lighter, and the faintest trace of a smile tugged at his lips.
The vendor chuckled as he handed over the taiyaki. "Ah, young couple out enjoying the festival, huh? Fresh off the grill—best when it's hot."
Shinobu didn't correct him. She simply took a bite, her eyes curling into half-moons. "It's really good! Giyu-san, try some."
She tore the taiyaki in half and held one piece to his mouth.
Giyu froze. The noise of the festival faded around him.
The red bean filling steamed between them, a little bit stuck to the corner of her lips.
He raised his hand and gently wiped the smear away with his fingertip before taking a bite of the piece she offered.
The flavor spread through his mouth—sweet, but not cloying. It was warmer than he expected.
"Good?"
Shinobu looked at him, her eyes sparkling.
"Yeah," he replied softly. "Sweeter than the red bean soup at the Butterfly Mansion."
They strolled along as they ate. Shinobu soon spotted a cotton candy stall and bought a pink one, holding the fluffy cloud in both hands.
When they reached the ring-toss booth, her eyes lit up. "Let's play this! I want that butterfly ornament!"
Giyu paid for the rings and watched as she took aim.
She missed again and again—the bamboo rings bouncing off the edges of the prize each time. Puffing her cheeks, she sighed. "Why can't I ever hit it…"
Giyu took one of the rings from her and stepped beside her. "Keep your hand steady. Aim for the base, not the middle. Use your wrist when you throw."
He gently guided her wrist, adjusting her angle.
"Try now."
With his hand still lightly over hers, Shinobu threw the ring again—
The bamboo ring traced a perfect arc through the air and landed cleanly over the butterfly ornament.
"I got it!"
Shinobu jumped up in delight, turning to grab Giyu's arm. "Yes! Thank you, Giyu-san!"
Giyu's body stiffened for a moment before he gently patted her shoulder. "It's nothing."
His eyes fell on the butterfly ornament in her hands—it matched the butterfly embroidery on her kimono perfectly.
"Giyu-san! Shinobu-san!"
A familiar voice called out. They turned to see Kamado Tanjiro and Tomioka Tō running toward them, each holding a skewer of candied fruit.
Tanjiro's face was dusted with sugar, while Tō had a pinwheel spinning in his hand. When they noticed the two, both slowed down awkwardly.
"You're here for the festival too?"
Tanjiro waved cheerfully, his eyes catching on the ornament in Shinobu's arms. "That butterfly ornament looks amazing! Did you win it at the ring toss?"
"Yup!"
Shinobu nodded proudly and held it up. "Giyu-san helped me get it!"
Tō glanced between them, then whispered, "Giyu-san, Shinobu-san… are you two… on a date?"
Giyu's ears turned red instantly, and just as he opened his mouth, Shinobu grinned and answered first. "Yes, we are. What about you two? Why are you here?"
"We came to buy something!"
Tanjiro lifted his skewered fruit with a grin. "The Kakushi said there's a stall selling special wisteria candy. We're buying some for everyone back at the Mansion!
Oh, right—Giyu-san, can you teach me the rhythm of Hinokami Kagura again during the next training? I still don't feel like I've got it right."
"Of course," Giyu replied calmly. "After the festival, starting next Monday."
"Great!"
Tanjiro bounced on his feet, then tugged on Tō's arm. "Then we'll leave you two to your date! See you later!"
They disappeared into the crowd, leaving Shinobu looking at Giyu, whose ears were still flushed.
She chuckled softly. "So, Giyu-san does blush when people call it a date?"
Giyu cleared his throat, trying to change the subject. "The fireworks are about to start. Let's go to the riverbank—the view is better there."
The riverbank was already crowded with townspeople, but Giyu found a quiet corner. He motioned for Shinobu to stand closer to the inside while he stood outward, shielding her from the bustling crowd.
Moments later, a golden firework burst open across the night sky.
Then came red, pink, and blue blooms one after another, lighting up the darkness and reflecting on Shinobu's face.
She gazed upward, her eyes shimmering with the fireworks' glow, brighter than the lights themselves.
Giyu didn't look at the sky—his gaze stayed on her.
Her lips curved into a faint smile, her hair lifted slightly in the night breeze, and the butterfly hairpin glimmered under the lantern light.
"Giyu-san, look! That blue firework—it looks just like your Water Breathing! Isn't it beautiful?"
She pointed upward, turning toward him.
Giyu followed her gesture. The blue firework rippled outward like a swirling current—it really did resemble his technique.
He turned back to her, his voice soft. "Yeah. It's beautiful. But not as beautiful as you."
Shinobu froze for a moment, her cheeks warming as her heartbeat quickened.
She looked up at him—his expression was completely sincere, no trace of teasing.
In his eyes, reflecting the light of the fireworks, was a quiet gentleness that flowed like the river beneath them.
"Giyu…"
She had just begun to speak when another explosion filled the sky—
the largest firework yet, golden light cascading across the river, illuminating both of their smiling faces.
When the fireworks ended, Giyu walked Shinobu back to the Butterfly Mansion.
At the entrance, she turned to face him, still holding the butterfly ornament in her hand. "Thank you for today. I had a wonderful time."
"So did I," he said with a small nod. Then he reached into his haori and took out a small box. "Here. This is for you."
Shinobu opened it—and inside was a silver ring engraved with delicate ripples and a tiny butterfly, perfectly matching her hairpin.
"This is…" Her voice trembled slightly.
"I had Hotaru Haganezuka make it when I visited the Swordsmith Village," Giyu said, sounding a little nervous. "If you don't like it—"
"I love it!"
Shinobu interrupted him with a bright smile and slipped the ring onto her ring finger. It fit perfectly. "I really love it."
She stepped forward and wrapped her arms gently around his waist. "Next festival, let's go together again, okay?"
Giyu stiffened for a moment, then slowly returned the embrace. "Okay," he said softly.
When Shinobu finally let go, she turned and ran toward the mansion. At the doorway, she looked back and waved. "Take care on your way home!"
Giyu stood there for a long while, watching the warm light from the Butterfly Mansion. He could still feel the lingering warmth of her touch on his hands.
He brushed his fingers over his ear—it was still warm—and a quiet smile tugged at his lips.
This summer night felt warmer than any Water Breathing practice he'd ever done.
The moonlight stretched across the small country road, lengthening his shadow—
and the quiet affection he carried, hidden in the calm ripples of his heart, was carried gently away by the summer wind.