Peach Mountain — a quiet, secluded place nestled in the misty highlands. In the courtyard of a wooden house built into the mountainside, the air was peaceful, broken only by the occasional chirping of birds.
"Lucas, I'm back…" Zenitsu's weary voice broke the silence. His shoulders drooped, his words slurred, and his face was swollen with bruises.
Sitting in the center of the courtyard, a young man with a handsome and refined appearance slowly closed his book and turned toward the voice. His expression didn't change — as though he had already predicted this outcome.
"Caught and dragged back again, huh?"
Lucas let out a small sigh, looking at Zenitsu with a mixture of sympathy and helplessness.
Lucas was not a native of this world. In his previous life, he had been an ordinary office worker on Blue Star. One day, after working endless overtime, he collapsed at his desk. When he woke up, he found himself in a different world — the world of Demon Slayer.
The body he now inhabited belonged to a young orphan named Tomoya, though Lucas had since embraced his new identity.
Wandering the streets after arriving, he had encountered Zenitsu by sheer coincidence. Both of them were down on their luck, and over time, they formed a bond, relying on one another for support. That bond only deepened after the appearance of a certain man.
One fateful day, Zenitsu had gotten into trouble once again. He had fallen head over heels for a girl who turned out to be a swindler. After being tricked and saddled with a mountain of debt, loan sharks came knocking. Lucas had been racking his brain, wondering how to help his friend escape the mess.
Then, an old man with flowing white hair appeared out of nowhere.
He was Sangijima Jigoro — the former Sound Pillar of the Demon Slayer Corps.
Without any hesitation, the Old Man brought both Lucas and Zenitsu to Peach Mountain with the intention of training them to become Demon Slayers.
However, while Zenitsu showed some promise despite his cowardly nature, Lucas hit an unfortunate wall. No matter how hard he tried, he couldn't learn any Breathing Techniques. It turned out that he had absolutely no aptitude for cultivation. Meanwhile, Zenitsu had natural talent but lacked the willpower to endure harsh training. His past was filled with ridicule, and years of being looked down upon made him instinctively want to run away.
Even with Lucas's encouragement, Zenitsu's progress was slow. Over the past year, he had attempted to escape training at least a hundred times. Each time, without fail, the Old Man dragged him back — usually battered and bruised.
"Grandpa was waiting for me halfway down the mountain again," Zenitsu grumbled, wincing. "If he hadn't ambushed me… Ahh! Lucas, go easy with that ointment!"
Lucas gently applied the soothing balm to Zenitsu's battered face. After a full year on Peach Mountain, Lucas hadn't learned Thunder Breathing — but he had mastered the art of bandaging injuries.
"Hang in there. We're almost at the end of our time here," Lucas said, calculating the days in his mind.
In the original Demon Slayer storyline, Zenitsu only trained for one year under the former Sound Pillar before participating in the Final Selection.
Based on that timeline, the test should be happening in just a couple of days.
Lucas's expression became solemn. Unlike Zenitsu, who had the legendary Thunder Breathing First Form — Thunderclap and Flash — Lucas had nothing. No techniques. No special abilities. No strength.
In this dangerous world crawling with demons, Lucas was like a defenseless lamb.
Suddenly—
Ding!
"Detecting host's desire to slack off. Activating Friend System…"
Lucas's eyes widened in shock as the voice echoed inside his mind. He glanced at Zenitsu, who hadn't reacted at all.
Only he could hear it.
Finally… is this my cheat?
Lucas's heart pounded with excitement.
"Friend System successfully bound."
"System Function: By establishing a friendship with someone, you may randomly obtain rewards from them."
"Rewards may include comprehension, aptitude, talent, or specific skills. No race restrictions. The closer the friendship, the richer the reward."
"System ability unlocked: Investigation Technique."
Lucas took a deep breath.
Just by becoming someone's friend… I can steal—I mean, share—their abilities?
His hand, mid-application of ointment, froze slightly as he whispered to himself: "Investigation Technique — activate."
Suddenly, a status panel appeared before him.
[Host: Lucas]
Race: Human
Realm: None
Comprehension: Inferior
Aptitude: Inferior
Talent: None
Skill: Bandaging (Mastery)
"…Ouch," Lucas muttered with a twitching expression.
Everything about him — from comprehension to aptitude — was bottom-tier. It was no wonder he couldn't learn Thunder Breathing.
According to the system, both Comprehension and Aptitude had five levels: Inferior, Lower, Middle, Upper, and Super. He was at the very bottom.
There was no way forward through traditional cultivation. His only path to strength… was through friends.
Lucas turned to Zenitsu, his curiosity piqued. He activated the Investigation Technique once more.
[Name: Agatsuma Zenitsu]
Race: Human
Realm: Mizunoto
Comprehension: Upper
Aptitude: Upper
Talent: Echoing Ears (Absolute pitch. Can detect emotions from sounds and distinguish between humans and demons.)
Skill: Thunder Breathing First Form: Thunderclap and Flash (Mastery)
Lucas nodded in admiration.
Zenitsu's potential was astonishing. Despite his cowardice, he had mastered Thunderclap and Flash in just a year — a feat that required not just talent, but resilience. The technique proficiency system ranged from Beginner, Proficient, Mastery, to Divine. For Zenitsu to already be at Mastery, he was a hidden monster.
"How is friendship determined?" Lucas asked the system.
"Verbal acknowledgment is sufficient. Rewards are based on the level of intimacy."
Lucas's eyes sparkled. He looked at Zenitsu again — but this time, with a look so intense that Zenitsu flinched.
"Zenitsu," Lucas said seriously, "we're friends, right?"
Zenitsu paused, confused at the question. But then, memories rushed back.
He had met Lucas five years ago. Back when no one believed in him, when he was constantly being ridiculed and rejected — only Lucas treated him like a real person. Like a brother.
Zenitsu's eyes turned red with emotion.
"Of course, Lucas! We've always been best friends!"
Ding!
"Successfully added Agatsuma Zenitsu as a friend."
"Detected friendship level: Best Friend. You may obtain four rewards."
"Reward 1: Comprehension — Upper."
"Reward 2: Aptitude — Upper."
"Reward 3: Talent — Echoing Ears."
"Reward 4: Skill — Thunder Breathing First Form: Thunderclap and Flash (Mastery)"
"Would you like to merge now?"
Lucas didn't respond right away.
No rush, he thought. I should merge these alone, just in case there's a side effect.
He felt giddy. These four rewards would completely transform him. He was no longer a cripple in this world — he now possessed both skill and potential. Even if he hadn't trained traditionally, these abilities would let him fight on equal footing with Zenitsu.
This Friend System is insane…
Lucas's confidence surged. While his realm was still low, that could be raised with time. In the Demon Slayer world, realms moved quickly. Zenitsu and his peers reached Pillar-level strength within two years.
As long as he kept forming meaningful friendships, Lucas believed he would surpass even the strongest swordsmen in the Corps.
"Lucas? You okay?" Zenitsu waved a hand in front of his friend's face.
"Huh? Yeah, I'm fine," Lucas smiled, snapping out of his daze. "The ointment's all done. You should rest up. We still have training tomorrow."
Zenitsu slumped instantly.
"Ugh… training…"
He trudged toward his room with heavy steps, dragging his feet as if he were walking to his own execution.
Lucas, on the other hand, moved lightly and energetically, barely suppressing the joy in his heart.
He had waited a full year on this mountain. At last… the real story was about to begin.
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