"Cough, cough! It stinks! My eyes are burning!"
Zenitsu and Tanjiro were both drenched in the foul-smelling medicine, lying miserably on the ground.
Tsuyuri Kanao, sitting opposite them, didn't have a single drop on her. She still wore the same calm, almost absent-minded expression, her breathing perfectly steady.
"Too fast… I can't see Kanao's movements at all. It's not just her hand speed—her prediction is flawless!" Tanjiro wiped the medicine from his face, filled with frustration and shock.
"I say, are you guys playing house?"
Just as the three of them were feeling discouraged, a very lazy voice drifted in from the far end of the porch.
Rin slowly walked over, holding a cup of hot tea.
Today he wore a very casual black yukata, with a lightning-patterned sword casually tucked into his waist, giving off a relaxed yet oppressive presence.
"Rin San!!"
The moment Tanjiro saw Rin appear, his eyes lit up instantly, as if he had just seen a savior.
His admiration for Rin had reached its peak ever since that single sword strike on Natagumo Mountain.
"Waaah, Boss Rin! This isn't training, it's pure abuse!" Zenitsu immediately crawled over and tried to hug Rin's leg, only to be kicked aside with obvious disgust.
"You can't even handle a little girl, and you still have the nerve to cry about it."
Rin blew lightly on the tea leaves floating in his cup, walked over to Kanao, pulled a cushion closer, and sat down cross-legged.
"Come on, little Kanao. Play with me."
Kanao glanced at Rin and nodded obediently.
After half a month of interaction, she had developed a special sense of awe toward this man who had forcibly taken away her coin and completely changed Shinobu.
"Oh my. Rin san is going to participate himself?!" Tanjiro's eyes widened, and he unconsciously held his breath.
"Ready, start!" Kanzaki Aoi called out as the referee, suddenly chopping her arm downward.
Swish!
The moment Aoi finished speaking, Kanao's hand shot out like lightning, reaching for the nearest cup of medicine with astonishing speed.
This was the terrifying reflex granted by Total Concentration Breathing: Constant!
However..
Tap.
A faint, crisp sound.
Just as Kanao's fingers brushed the side of the cup, another hand had already moved. Though it seemed to start later, it arrived first, lightly pressing down on the back of her hand.
How is that possible?!
Kanao's pupils shrank. She hadn't even seen an afterimage.
She immediately tried to switch targets and grab a second cup, but no matter how fast she moved, Rin's hand was like a prophetic phantom, always arriving a fraction of a second earlier to pin down her choice.
Tap! Tap! Tap!
Three consecutive attempts were all effortlessly suppressed.
"Too slow."
Rin chuckled, casually flicking his finger. The wooden cup filled with medicine instantly flew into his palm.
He didn't splash it at Kanao. Instead, with a mischievous flick of his wrist...
Splash!
The entire cup of pungent medicine flew over Kanao's head and splattered all over the face of Zenitsu, who had been stretching his neck behind her to watch the show.
"AAAAAH! Why me?!" Zenitsu shrieked miserably.
Rin set the empty cup down. Seeing Tanjiro's stunned expression, he explained,
"See? This is called absolute reaction suppression. The reason little Kanao can crush you so easily is because she maintains Total Concentration Breathing twenty-four hours a day—even while sleeping. That's called 'Total Concentration: Constant.'"
"Total Concentration… Constant?" Tanjiro repeated, stunned.
"Breathing techniques don't just allow you to unleash power beyond your limits in an instant. When maintained over a long period, they can also fundamentally transform the body's basic physical attributes."
Rin stood up, walked to the edge of the porch, picked up a specially made, hard large gourd, and tossed it into Tanjiro's arms.
"If you can't even master this most basic constant technique, then when you face the Twelve Kizuki, you won't even be fit to get stuck between their teeth."
"Starting today, besides the regular stretching exercises, the three of you will blow into these gourds every day. Only when you can burst these hardened gourds using nothing but your lung capacity will your 'Constant' be considered barely entry-level."
Rin issued the training targets with complete authority, effortlessly taking over the role of instructor.
Looking at the large gourd in his arms that produced a dull thump when tapped, Tanjiro swallowed nervously. Yet his eyes soon filled with determination.
"I understand! I'll definitely do it! Thank you for the guidance, Rin san!"
"Rin."
At that moment, Shinobu Kocho stepped out from the inner courtyard, holding a piece of freshly delivered stationery. Her expression had turned unusually serious.
She quickly walked over to Rin and spoke in a low voice that only the two of them could hear.
"The Kasugai Crow has brought back confirmed intelligence... Traces of a demon have appeared on the Mugen Train. The Master has already ordered the Flame Hashira, Kyojuro Rengoku, to head there and investigate."
"So it's finally begun."
Hearing this news, Rin immediately realized that the Mugen Train incident had officially started.
"Tell Rengoku san not to worry," Rin said calmly. "When the time comes, I'll go with him and take part in the investigation."
...
BOOM—!
Accompanied by a heavy explosive sound, the rock-hard, specially made medicinal gourd finally shattered into a spray of fragments as Kamado Tanjiro's face flushed red and he blew with all his strength.
"Whew… whew… I did it! Rin-san! I finally blew up the largest gourd!"
Tanjiro braced his hands on his knees, panting heavily. Sweat had soaked through his thin training uniform, but his dark red eyes shone with an unprecedented excitement.
After several days of brutal training under Rin's Spartan-style, high-pressure supervision, he had finally engraved the technique of Total Concentration: Constant into his body's instincts.
On the other side, although Agatsuma Zenitsu and Hashibira Inosuke were still rolling their eyes while trying to blow into medium-sized gourds, they were already able to maintain the breathing technique around the clock without interruption.
"Barely a passing grade."
Sitting on the corridor railing, Rin casually tossed a half-eaten apple into the trash bin, then stood up and clapped his hands.
"Since the foundation is more or less set, pack your things and get ready to move out. There's work tonight."
"There's work? Could it be…" Tanjiro suddenly looked up, clenching his fists.
"The Master has issued new orders. Large-scale civilian disappearances have been reported on the Mugen Train. The Flame Hashira, Kyojuro Rengoku, has already departed for the station in advance."
Rin stepped down the stairs, casually took a pure black haori from a wooden rack, and draped it over his shoulders.
"You three, bring your Nichirin blades and follow me. Let me see how much you've actually improved during this time. If your performance is too pathetic, I'll kick you off the moving train on the spot."
"A-A train?! Why do we have to go to a place like that?!" The moment Zenitsu heard they were going on a mission, he clutched his head in terror.
Inosuke, however, snorted two streams of white vapor from his nostrils. "I don't care if it's a train or a waterwheel! As long as it's prey, this great Inosuke Hashibira will cut it all down! Boar Rush!"
Looking at the noisy trio, Rin didn't bother responding and simply walked toward the front courtyard of the Butterfly Mansion.
As he passed through the long corridor of the inner courtyard, a petite figure blocked his path.
Shinobu stood quietly beneath the massive wisteria tree, holding a small package in her hands.
Tonight, she wasn't wearing her Demon Slayer Corps uniform. Instead, she had changed into a simple yet elegant light-purple outfit. The night breeze stirred her smooth black hair, making her look unusually gentle.
"You're leaving?" Shinobu looked at Rin as he approached, her voice softer than usual.
"Yeah. I'm heading to the Mugen Train. There's a high chance one of the Twelve Kizuki is hiding there after all." Rin stopped and reached out to take the package she offered.
"Inside are some specially made wound ointments, blood-clotting powders, and… rice balls I made myself."
Shinobu turned her head slightly, seemingly unwilling to meet his eyes. Her usually cool voice carried a rare trace of tsundere stubbornness.
"Don't misunderstand. The rice balls are only because I'm worried you might starve to death on the way and embarrass the Butterfly Mansion. As for the medicine… a reckless brute like you would do best never needing it. Hmph!"
Rin weighed the still-warm package in his hand, and the corners of his mouth curved upward.
He didn't reply. Instead, he suddenly stepped forward and reached out with his free hand, wrapping his arm around Shinobu's slender waist and pulling her into his embrace.
"H-Hey! What are you—mmmph.."
Before Shinobu could finish speaking, Rin had already lowered his head and pressed his lips against hers.
_____
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