Ren Kuroda and Rui held fundamentally different views of family.
Ren believed family was irreplaceable. Protection shouldn't be a one-sided demand; one should also consider what they could do to safeguard those they loved.
Rui's so-called "family love," on the other hand, was a ceaseless appetite for taking. In his mind, being family meant others existed solely to protect the youngest among them.
Provoked by Ren's words, Rui's composure snapped. Enraged, he lunged at Ren.
Even as a member of the Twelve Demon Moons, an elite-tier demon, the gap between him and Ren was catastrophic. This battle was far less suspenseful than Spider Princess versus the Spider Father.
Rui's crimson spider silk, sharp enough to slice through Nichirin Blades, felt like flimsy rope against Ren's strikes. Even when Rui reinforced his web with his Blood Demon Art, it was powerless against Ren's swings.
The crescent-shaped slash, glowing with a vibrant purple aura, shot forth from Ren's blade like lightning unleashed. Wind swept through the mountains, expanding the strike into a devastating arc.
The web, painstakingly woven from countless blood-red silks, shredded like paper before the attack. The force didn't stop there—it carved a deep trench into the forest floor.
Rui's eyes widened in disbelief. His ultimate Blood Demon Art, capable of cutting through swords, was so effortlessly destroyed. His confidence evaporated instantly.
For the first time, he realized why his so-called family couldn't stop this opponent—the demon-slaying swordsman before him was unlike anyone he had faced before.
Narrowly avoiding the next flying slash, Rui felt the air tear past him, trees crashing behind him. Fear flickered across his pale face.
"The howl of divine wind… the momentum of a force that can scatter armies… as swift as the wind itself—a true army-breaking gust!"
Before Rui could recover, a second strike appeared, invisible to the naked eye. The wind that accompanied Ren's blade was sharp enough to slice skin, moving faster than thought.
The last thing Rui saw was a silver streak in the air.
It was over before he could even register pain. His head was gone.
Ren, as calm as ever, slowly sheathed his blade. To him, the act felt almost trivial.
The gap in power was immense. Why was his opponent so strong? Perhaps it was the strength born of Ren's desire to protect his family.
In those final moments, Rui's memories returned like a tidal wave. Before becoming a demon, he had been a frail, sickly boy who had admired the story of a father sacrificing himself to save a drowning child. He had wondered if his own parents would have done the same.
Then Muzan Kibutsuji entered his life, offering blood and power. Rui's human frailty vanished, replaced by the monstrous existence of a demon.
His parents, overwhelmed with horror at what he had become, had tried to kill him to atone for their sins, intending to die alongside him. But Rui, consumed by rage and confusion, killed his own father in retaliation.
He had convinced himself that their love was hypocritical. No one in the world would willingly harm their child.
Only when his mother confessed the truth—revealing their intention to die together—did Rui understand. But the revelation was too much. Overcome with guilt, he had subconsciously suppressed the memory and fled to Mount Natagumo.
Now, decapitated by Ren's Nichirin Blade, Rui's past came flooding back. In truth, he should have died with his parents. He had destroyed his family bonds and tried to seek comfort in false emotions. It was, in every sense, laughable.
"Will you protect your family… and make sure they aren't hurt?"
Rui, his body half-charred, asked slowly, watching Ren walk away.
"Of course," Ren said, his voice steady, unwavering. "If it's to protect them, it doesn't matter whether I become a demon or not."
His answer reflected his unshakable resolve—not as a demon lord, but as someone willing to sacrifice anything for his family.
Hearing the reply he wanted, Rui allowed a faint, final smile to cross his lips.
"It seems… you truly love your family. I'll be reunited with mine soon…"
Then, his body turned entirely to ash. Ren looked at the spot where Rui had vanished, silently turning away.
"Kibutsuji Muzan… you really are a terrible person," he muttered.
With Rui, Lower Moon Five, eliminated, Ren had completed his mission. Rewards arrived almost immediately, including news that he could leave this world. He could stay temporarily, but the maximum time allowed was one month.
Exceeding the limit would require spending reputation points—an astronomical 100 points per day.
Thanks to the mission, Ren's reputation points had increased, but even so, the price for staying longer was staggering. When he first arrived, his battle at Fujikasayama had completely depleted his points. Joining the Demon Slayer Corps had helped him rebuild his reputation, but transforming Spider Princess had cost him significantly.
Now, counting the rewards from his latest mission, Ren Kuroda had 900 human reputation points and 500 demon reputation points.