Five days later — Butterfly Mansion, training room.
Warm sunlight filtered through the overhead skylight, casting golden rays across the floorboards of the training room. Despite the serene beauty of the scene, the air crackled with tension, thick with spiritual pressure and intensity.
Clang! Clang!—
In the center of the room, Lucas and Kochou Shinobu engaged in a fierce training duel. Their Nichirin blades moved with blinding speed, their strikes sharp and clean, the rhythm almost musical—like a deadly dance.
Sparks flared each time their blades collided.
Electric arcs radiated from Lucas's blade. Each swing of his sword came with a heavy roar of compressed thunder, the golden energy crackling wildly through the air. His movements were so fast that his blade's path became a blur—nearly impossible to track.
Across from him, Shinobu wielded her pink Nichirin blade with grace. It was long, slender, and curved like a needle—elegant and precise, much like herself. Though she lacked Lucas's explosive speed, her footwork was exceptional. Her movements were like a butterfly's—light, graceful, impossible to pin down.
The training room was filled with gusts stirred by their swordplay.
Lucas missed a strike and swiftly transitioned into a new form, his blade trailing electric arcs. Shinobu, recognizing the incoming danger, pivoted on her foot and thrust her blade toward Lucas's chin.
But Lucas simply smiled.
A subtle expression, calm and confident.
"That look..."
Shinobu immediately became alert. She'd seen it before.
For the past few days, Kanao had trained Tanjirou, Zenitsu, and Inosuke, while Shinobu had taken personal responsibility for Lucas's training.
And on their very first day, she was caught off guard.
She hadn't thought much of him at first. During Lucas's battle with Shinazugawa, he'd held his own, but she attributed most of that to his natural talent and perseverance.
But once she crossed blades with him herself—she realized something shocking.
He had evolved.
His breathing techniques, his speed, his power—everything had improved drastically, almost alarmingly, in a matter of days.
If she weren't a Pillar herself, she might have been overwhelmed by him right from the start.
Now, with experience from their recent matches, Shinobu immediately knew that her thrust wouldn't land. She fluidly altered her attack mid-motion, turning it into a swift slash toward Lucas's shoulder.
Lucas reacted just in time, blocking the strike horizontally. But then, his blade shimmered—and its color shifted from electric gold to a deep blue.
Water Breathing.
Smooth, seamless, and flowing like a river.
His strikes suddenly changed rhythm—becoming continuous, elegant, and unpredictable.
Shinobu frowned slightly as she withdrew her blade to regroup.
"Water Breathing? Again?" she thought. "When did Lucas learn this form?"
Though his strength still fell short of hers, Lucas was far more troublesome than any demon she had faced.
His shifting breathing styles, combined with his unmatched speed and unpredictable attacks, gave her a massive headache.
As she stepped back, Lucas's eyes flashed with a hint of regret.
If she'd been even a second slower... I could have disarmed her.
And a Demon Slayer without a Nichirin blade?
Even a Pillar would be significantly weakened.
But Lucas didn't dwell on it. If he could defeat a Pillar that easily, it would mean Pillars were far weaker than expected—and that wasn't the case.
They both resumed their stances, their shadows stretching and intertwining under the sunlight. Then, in a blur of movement, they clashed again—sword to sword, light and shadow blending as they danced across the training floor.
Watching from the sidelines were Tanjirou, Zenitsu, and Inosuke, their expressions frozen in awe.
"Wha… Lucas can fight Miss Shinobu on even ground?" Tanjirou exclaimed, eyes wide.
He wasn't the same wide-eyed novice anymore. He understood very clearly how powerful Pillars were—and Kochou Shinobu was no exception. Her strength wasn't just about brute force—it was in her deadly poison techniques and surgical precision.
"Lucas has gotten stronger again. Is awakening really this powerful?" Zenitsu murmured, his jaw hanging open.
He could still see Shinobu's form clearly—but Lucas?
Only golden streaks of lightning remained in the air whenever he moved.
"That bastard! I want a duel!" Inosuke roared, steam puffing from under his boar mask.
He had been brooding ever since his loss against the Spider Demon Father. The defeat had hit him harder than he'd expected.
But everything changed on the third day.
Lucas had visited him, walked up to him with calm confidence, and in front of everyone, blew up a gourd the size of his head with a single breath.
Then, he patted Inosuke on the head and smirked.
"If you're weak... train harder."
Those words struck deeper than any sword.
Inosuke may not have understood fancy explanations, but that—he understood.
Since then, he trained harder than anyone else.
He even dreamed of twisting Lucas's head off in a match. It became his sole motivation.
Back on the field, the duel continued fiercely.
The final clash came when Shinobu performed Insect Breathing: Dance of the Hornet — True Flutter. Her blade flickered and danced like a blur, finally finding its mark and ending the session.
She lowered her sword, a cheerful but sincere smile forming on her lips.
"Not bad. Your mastery of switching between Breathing Forms has improved a lot."
She sheathed her blade and added, "If you learn one more style, even I might start getting overwhelmed."
Lucas smiled humbly. "You flatter me."
He had only revealed Water and Thunder Breathing so far—purposely holding back.
Showing off all his Breathing Forms at once might attract Muzan's attention, and Lucas was nowhere near ready to face that monster.
"You seem to be in good spirits today, Miss Shinobu. Did you work through something troubling you?"
"Eh?" Shinobu blinked, surprised.
Was she really that obvious?
She had, in fact, experienced emotional relief the night before. After talking with Tanjirou about her sister and her long-held sorrow, the burden in her heart had lightened for the first time in years.
She expected Tanjirou to notice—after all, his nose was sharp and could sense emotions.
But how had Lucas figured it out?
"You're right, actually. I feel… better." she admitted, her smile more natural this time. There was no trace of the usual façade she wore. Instead, a quiet gentleness radiated from her expression.
Lucas took his chance.
"Then, Miss Shinobu—would you be willing to be friends with me?"
Shinobu froze again.
But then her eyes softened. Her smile turned into something warmer, more genuine.
"Of course."