Prelude to the Mugen Train

Afternoon sunlight filtered through the paper doors of the Butterfly Mansion, casting dappled patterns across the floor. The air was filled with the mingled scents of herbs and sweat, accompanied by Tanjiro and Inosuke's heavy breathing.

In one corner of the courtyard, Tanjiro and Kanao Tsuyuri sat facing each other, their palms held opposite each other with a thin, almost invisible black halo between them. They were trying to coat their palms in Armament Haki and practice a delicate contest of strength. The veins on Tanjiro's forehead bulged. He was clearly struggling to control it, his Haki flickering like a candle in the wind. Kanao, meanwhile, was much steadier. Her pink eyes focused intently on her palm, where the black halo was even and solid.

"Tanjiro, concentrate. Imagine the energy flowing like water, covering your entire palm. Don't let it come and go." Moyu's voice rang out calmly from where he stood beside them, his Six Eyes precisely tracking every slight change in their energy flow.

"Yes, Moyu!" Tanjiro gritted his teeth and tried to adjust his breathing, striving to calm the unruly energy.

On the other side, the scene was entirely different.

"Aaah! Damn it! Damn it all! Why won't it work?! My energy won't do what I tell it!" Inosuke flailed at a wooden training post, trying to coat his fist in Haki. But every time, the energy either dispersed or vanished with a puff, leaving nothing but a black dot on his skin. Furious, he screamed and slammed his head into the post.

"Ugh... this is so hard... and I'm so tired... My hands are almost cramping..." Zenitsu lay sprawled beneath the veranda, weakly shaking his wrists. He had just tried to coat his Nichirin Blade in Haki, only to nearly lose his grip on the hilt and cut himself. "Are Tanjiro and Kanao Tsuyuri monsters...? How can they make it look so easy...?"

"You're just too lazy, Zenitsu!" Aoi said as she walked past with a medicine box, criticizing him without mercy. "Look how hard Tanjiro and Miss Kanao Tsuyuri are working! And look at you, slacking off every day!"

"Boo-hoo... Aoi's so strict..." Zenitsu pretended to cry.

Moyu glanced at them but said nothing. Training in Armament Haki did require talent and patience; it couldn't be rushed. Tanjiro's tenacity and Kanao Tsuyuri's talent meant they were bound to progress a little faster, while Inosuke and Zenitsu's temperaments... needed more time to be tempered.

Just then, the sound of flapping wings drew closer. A Kasugai Crow flew across the courtyard and landed precisely on Moyu's shoulder.

"Caw! Urgent orders! Urgent orders!" the Kasugai Crow cried shrilly. "Mugen Train mission! Mugen Train mission! There have been multiple passenger disappearances recently, and more than forty people are missing! Demon Slayer Corps members sent to investigate have also lost contact one after another, including Kinoe-ranked members! The situation is critical! Kanoe-ranked members Tanjiro Kamado, Zenitsu Agatsuma, and Inosuke Hashibira are ordered to proceed to the Mugen Train at once and assist with the investigation! Proceed to the Mugen Train at once and assist with the investigation! Caw!"

The Mugen Train!

An azure light flashed in Moyu's eyes and vanished. Has it finally come...? A little sooner than I expected. Akaza... Upper Rank Three...

"The Mugen Train?" Tanjiro stopped practicing, his expression grave. "A lot of people have gone missing?"

"Even Kinoe-ranked members have lost contact?!" Zenitsu jumped to his feet in fright. "Wait! Why am I on the mission list?! I'm not going! Absolutely not! If even Kinoe-ranked members can't handle the demon, won't we just be going to our deaths? I haven't married Nezuko yet! Boo-hoo!"

"Wahahaha! Finally, a decent mission! Just watch me chop the demon on that train into pieces!" Inosuke, on the other hand, waved his two blades excitedly.

Moyu gently smoothed the Kasugai Crow's feathers and murmured to himself, "The Mugen Train... That really was fast."

His voice was quiet, but Shinobu Kocho, who had been keeping an eye on him, heard it. She approached carrying a tray of freshly prepared herbs, a question in her purple eyes. "What is it, Moyu? Is there a problem with this mission?"

Moyu looked at her and said calmly, "It's nothing. I'll go on this mission."

Shinobu paused. "You? But... Mr. Rengoku is already going on this mission. He's a Hashira, so he should be able to handle it." She remembered the mission briefing mentioning that the Flame Hashira, Kyojuro Rengoku, would be going as the main force.

"I know." Moyu nodded. "But it would still be better for me to go. This is a good chance... to verify a few things. He hasn't left yet, has he? I'll go explain the situation to him shortly."

Shinobu frowned slightly, keenly sensing something. "What about Tanjiro and the others?" She gestured toward the trio, who were still either cheering or wailing over the mission.

"This mission is too dangerous for them," Moyu said in a tone that brooked no argument. "Let them take other, relatively safer missions. They can use the chance to get accustomed to Total Concentration: Constant and Armament Haki. Leave the demon on the Mugen Train to me."

Shinobu fell silent for a moment, then stepped closer and lowered her voice, her purple eyes fixed on Moyu. "Moyu... did your eyes 'see' something again? About the Mugen Train's... future?"

Moyu met her gaze. He neither denied it nor fully admitted it, giving only a vague reply. "Yes. But... the fragments I saw were very blurry. I'm not sure." He couldn't tell her the truth. If he told Shinobu that Upper Rank Three, Akaza, would appear this time and that Rengoku would die at his hands, more than one Hashira would go. But if the other Hashira ganged up on Akaza, it might cause Muzan to start a group battle early. Without time to grow stronger, they could easily suffer a total wipeout. After all, although Akaza liked fighting strong opponents, he wasn't stupid. If he were being beaten up one-sidedly, he would definitely call for backup. At this stage, the Demon Slayer Corps was far from ready for a final showdown with the Upper Ranks, much less Muzan.

"Would it... be very dangerous for Mr. Rengoku to go, too?" A trace of almost imperceptible tension entered Shinobu's voice.

"Yes." Moyu's answer was brief and certain.

"Wouldn't it be even more dangerous for you?" Shinobu's frown deepened. "If even Mr. Rengoku might not be able to handle it..."

"In a head-on fight, I'm indeed no match for him," Moyu said honestly. "But staying alive shouldn't be much of a problem. No matter how strong an attack is, it means nothing if it can't hit." He had confidence in the defensive power of his Limitless, especially after fusing with the Sage Body and mastering Total Concentration: Constant, which had greatly improved his recovery and endurance in prolonged combat. Holding out until daybreak wouldn't be difficult, even though Akaza looked somewhat like Sukuna.

Shinobu recalled Moyu's strange, unpredictable defensive ability, which even Mr. Sanemi hadn't been able to break through. She felt a little reassured, but was still worried. "Should I go with you? Or... should we ask Mr. Sanemi or the other Hashira to come along? There's safety in numbers."

Moyu shook his head, his tone serious. "No. If too many Hashira-level fighters gather, the course of the future I 'saw' may shift drastically. It could very well cause... Muzan to notice prematurely, or even intervene himself. If that happens, the situation will spiral completely out of control. So we have to keep things 'as they were,' or at least make them look that way."

Shinobu fell silent. She knew full well how terrifying and cautious Muzan was. If a large-scale deployment of Hashira-level fighters tipped him off, it could indeed have disastrous consequences. She looked into Moyu's calm yet deep azure eyes and seemed to see a weighty resolve in them.

"...I understand." At last, she sighed softly. A gentle but worried smile returned to her face. "Then you must... be very careful. Once you've verified what you want to verify, come straight back. Don't push yourself."

"Mm. Don't worry." Moyu nodded.

He knew that Kyojuro Rengoku was cheerful and upright, and made it his duty to protect his juniors. As long as Moyu volunteered to go for some "experience" and suggested that Tanjiro and the others take more "suitable" missions, Rengoku would most likely agree.

A short while later, Moyu found Kyojuro Rengoku preparing to leave in an open area near headquarters. The Flame Hashira still wore his flame-patterned haori, and he was full of energy, his voice booming.

"Umu! It's you, Moyu! What can I do for you?" Rengoku greeted him with a smile.

"Rengoku, let me take the Mugen Train mission," Moyu said, getting straight to the point. "Tanjiro and the others have only just mastered Total Concentration: Constant and Armament Haki. They need safer missions to consolidate them. We don't know what's happening on the Mugen Train, and even Kinoe-ranked members have lost contact. It would be rather dangerous to send them. I happen to have some free time lately, and I'd like to get out for a while."

Kyojuro Rengoku folded his arms, raised a thick eyebrow, and looked Moyu over carefully. Then he burst into a hearty laugh. "Umu! That makes sense! Young Kamado and the others do indeed need more training! Since the Eye Hashira has volunteered, I'll leave this mission to you! I believe in your strength! Be sure to take care, find out what's happening, and keep the people safe!"

"Yes. Leave it to me." Moyu bowed slightly.

Things had gone more smoothly than he had imagined. Kyojuro Rengoku had absolute trust in his comrades, especially in a Hashira whose strength had been recognized.

Watching Kyojuro Rengoku turn and walk away, Moyu let out a quiet breath. A cold glint flashed through his azure eyes.

The Mugen Train, Lower Rank One Enmu, Upper Rank Three Akaza... perhaps... there would be other unexpected developments, too.