Peach Mountain, the courtyard of a wooden house halfway up the mountainside.
"Raiden, I'm back," Zenitsu said weakly, his head hanging low, his voice slurred.
The young man seated in the center of the courtyard heard Zenitsu's voice, closed the book in his hands, and turned around. One look was enough to tell him what had happened.
Zenitsu's face was swollen, bruised, and marked with fresh injuries.
"Caught and dragged back again?" Raiden asked calmly.
He rose to his feet, his expression holding a trace of helpless familiarity rather than surprise.
Raiden was handsome in a quiet way, sharp eyes softened by patience. He had already expected this outcome.
Raiden was not originally from this world. In his previous life, he had been an overworked office employee from another world, collapsing from exhaustion during late night overtime. When he opened his eyes again, he found himself in the world of Demon Slayers.
The body he had awakened in belonged to an orphan named Tomoya. Alone, with no family and no future, just like Zenitsu.
The two had met while drifting through the streets, clinging to survival. They relied on each other until the day everything changed.
Zenitsu had been tricked by a girl he fell for, leaving him buried in debt. When the collectors came knocking, Raiden had been desperately searching for a way out.
That was when an elderly man with white hair appeared.
Jigoro Kuwajima, the former Thunder Hashira.
The old man took them both back to Peach Mountain, intending to train them into members of the Demon Slayer Corps.
But things did not go as expected.
Zenitsu possessed rare talent, yet years of ridicule had crushed his confidence. Fear ruled him, making every step forward a battle against himself.
Raiden, on the other hand, had no talent at all.
No matter how hard he tried, no matter how many times he trained, he could not grasp any Breathing Technique.
While Zenitsu struggled to face his fear, Raiden struggled against his own limitations.
During the year on Peach Mountain, Zenitsu attempted to flee more times than either of them could count. Every attempt ended the same way, with Jigoro waiting patiently on the mountain path, dragging him back battered and bruised.
"This time he was already waiting at the trail," Zenitsu muttered through clenched teeth. "If not for that, I almost made it. Ah, it hurts. Raiden, easy, please."
Raiden sighed and carefully applied ointment to Zenitsu's face.
He had not learned Thunder Breathing, but he had become very skilled at treating injuries.
"Relax," Raiden said quietly. "We're almost there."
He calculated the time silently.
In the Demon Slayer Corps, Zenitsu trained for only one year before entering the Final Selection. If Raiden remembered correctly, that moment was close. Very close.
That thought filled him with unease.
Zenitsu would survive. His Thunder Breathing First Form alone was enough to carve a legend.
Raiden was different.
He had no Breathing Style, no strength, no protection. In a world filled with demons, surviving even a single night would be a blessing.
Then, suddenly, a sound echoed in his mind.
"Ding."
"Detected host's strong desire to avoid a miserable death. Friend System binding in progress."
"Binding successful."
Raiden stiffened.
Zenitsu stared at him, confused, clearly unaware of the voice.
Only Raiden had heard it.
His heart raced.
Suppressing his excitement, Raiden waited.
"Friend System function unlocked. By forming friendships, the host may randomly obtain abilities from the target."
"Rewards may include comprehension, physical aptitude, talents, and skills."
"No race restrictions."
"The closer the bond, the greater the rewards."
"Additional ability unlocked: Investigation."
Raiden's fingers slowed as he applied the ointment.
He immediately used Investigation on himself.
Name: Raiden
Race: Human
Rank: None
Comprehension: Inferior
Aptitude: Inferior
Talent: None
Skill: First Aid and Bandaging, Mastery
Raiden's lips twitched.
So that was why.
Comprehension and aptitude were ranked from Inferior, Lower, Middle, Upper, to Super.
He was at the very bottom.
This body was never meant to wield a sword.
He shifted his gaze to Zenitsu.
Name: Agatsuma Zenitsu
Race: Human
Rank: Mizunoto
Comprehension: Upper
Aptitude: Upper
Talent: Echoing Hearing, the ability to perceive emotions and distinguish demons by sound
Skill: Thunder Breathing First Form, Thunderclap and Flash, Mastery
Impressive.
Even Raiden had to admit it.
Upper comprehension, Upper aptitude, and mastery over Thunderclap and Flash in less than a year. Zenitsu was a monster who did not realize his own strength.
"How is a friendship confirmed?" Raiden asked silently.
"Verbal acknowledgment is sufficient. Rewards are based on mutual bond."
Raiden looked at Zenitsu, his eyes shifting subtly.
Zenitsu felt it immediately. His throat tightened.
"Why are you looking at me like that?" Zenitsu asked, suddenly nervous.
Raiden smiled faintly.
"Zenitsu," he said casually, "we're friends, right?"
Zenitsu froze.
Then he nodded fiercely.
"Of course we are."
Five years ago, when everyone else mocked him, Raiden had treated him like a normal person. Without Raiden, Zenitsu doubted he would have survived that long.
"Ding."
"Agatsuma Zenitsu added as a friend."
"Bond level detected: Best Friend."
"Four rewards available."
Comprehension: Upper
Aptitude: Upper
Talent: Echoing Hearing
Skill: Thunder Breathing First Form, Thunderclap and Flash, Mastery
"Merge now?" the system asked.
"No."
Raiden refused immediately.
He needed privacy.
Even without merging, warmth spread through him.
This system was absurdly powerful.
With enough friends, even someone like him could stand on equal footing with the strongest.
"Raiden, are you sure you're okay?" Zenitsu waved a hand in front of his face.
"I'm fine," Raiden replied, stepping back. "The ointment's done. Go rest. Training's tomorrow."
Zenitsu's shoulders slumped instantly.
"…Right."
Dragging his feet, Zenitsu returned to his room.
Raiden walked away quietly, his steps light for the first time since arriving in this world.
At last, he had a way forward.