For the final days they spent in this world, Akira and Erika decided to meet everyone who had helped them along the way, to say their goodbyes and tie up any loose ends that remained.
The first place they went was Tamayo's residence.
Before anything else, they gathered Shinobu and headed there together. Tamayo greeted them with a gentle smile, and for once, Yushiro was not glaring at them as if they were mortal enemies.
Akira didn't waste time.
"So," he asked, looking at Tamayo, "did you finish the medicine I asked you to make?"
Tamayo nodded calmly. "Yes. Your formula was surprisingly easy to follow, even though the process itself was quite sophisticated."
As she spoke, she placed a small vial filled with red liquid on the table in front of him.
Erika leaned forward, curiosity lighting her eyes. "A new potion? What does this one do?"
Akira glanced at the vial and answered matter-of-factly, "It suppresses hyper-activated mitochondrial respiration, down-regulates stress-induced gene expression, stabilizes runaway mitotic cycles, and permanently seals the neural-endocrine feedback loop responsible for Demon Slayer Mark manifestation."
Erika stared at him.
"…Speak human."
Akira sighed, already expecting that reaction.
"You remember the Demon Slayer Marks, right?" he said. "The ones that massively increase your power, but shorten your lifespan?"
Erika nodded.
"This medicine reverses that," Akira continued. "It heals the damage the Mark causes to the body… and then it closes the door completely, so your body can never activate it again."
Erika blinked. "So if someone drinks this… the effects of the Demon Slayer Mark disappear, and they can never use it again?"
"Yes," Akira replied without hesitation. "I made it so everyone could activate their Demon Slayer Mark during the fight. That means I'm responsible for returning them to normal afterward, too."
Akira turned his gaze toward Shinobu.
"So, Shinobu-san," he said casually, "are you willing to be my test subject?"
Shinobu let out a tired sigh. "Fine. Whatever." She picked up the vial and glanced at it. "So I just drink it? Like normal medicine?"
"Yes," Akira replied. "Normally."
Under the curious gazes of everyone present, Shinobu raised the vial and drank the red liquid in one smooth motion.
And then.
Nothing happened.
They waited.
A few seconds passed. Then a few more.
No sudden pain. No glowing marks. No dramatic reaction of any kind.
Erika tilted her head. "Did it… not work?"
Akira frowned slightly, confused. "Huh? I think it worked just fine, though."
"But nothing happened," Erika pointed out.
Akira looked at her. "It's medicine. Does something visibly happen every time you take your medicine?"
Erika thought, "Normally, no. But this one was created by you."
She folded her arms. "So does it work or not?"
"We can test it," Akira said calmly. He turned back to Shinobu. "Shinobu-san, can you try activating your Demon Slayer Mark?"
Shinobu nodded and focused, attempting to draw it out the same way she had during the battle.
Nothing happened.
She tried again.
Still nothing.
After a moment, she opened her eyes. "I can't activate it."
Akira nodded. "Then the medicine works." After a brief pause, he added, "Though it would be more reassuring if we conduct a few tests, just to be sure."
And so they did.
Several examinations later, all signs pointed to the same conclusion: the medicine was completely safe, and it had done exactly what Akira intended.
Satisfied, Akira turned back to Shinobu. "Shinobu-san, wasn't there a Hashira meeting today?"
"Yes," Shinobu replied. "There is."
"Then could you take these to the other Hashira?" Akira said, gesturing to a box filled with identical vials. "I'll deliver Tanjiro's myself. What do you say?"
Shinobu raised an eyebrow. "But you're supposed to attend that meeting too."
"I will," Akira replied. "But you all gather way too early. I figured it would be more efficient if you distributed these during that time."
She sighed. "There is a time and place for this… but fine."
She picked up the box filled with the medicine and turned to leave.
Soon after, Shinobu departed, leaving Akira and Erika alone with Tamayo and Yushiro.
After a brief silence, Tamayo looked at them gently.
"So… are you two leaving?" she asked.
Akira nodded. "Yes. Soon, we'll be leaving." He paused, then added, "That's why we wanted to say a proper goodbye."
Both Akira and Erika bowed slightly.
"Thank you for your help throughout this journey," Akira said sincerely.
"Yes," Erika agreed. "You helped us so much. Without your help, we couldn't have had such an easy time here."
And it was true. Tamayo and Yushiro had helped Akira with medicines and poisons, and they had guided Erika in learning Blood Demon Arts. Because of that support, their mission had gone far more smoothly than it otherwise would have.
Tamayo shook her head softly. "No. I should be the one thanking you." Her voice carried deep emotion. "You helped me achieve my long-standing dream. Without you, I don't know how many more years it would have taken to defeat Muzan."
Yushiro crossed his arms and spoke up as well. "You guys did what you promised. You're amazing."
Akira and Erika froze.
They both stared at Yushiro in shock.
"Yushiro-san… are you feeling okay?" Erika asked carefully.
Akira squinted at him. "Who are you, and what did you do to Yushiro?"
Yushiro's face immediately turned red. "I was kidding! Don't take my words so seriously!" he snapped.
That only made everyone else laugh.
After the laughter died down, Akira asked, "So now that Muzan is dead, and the demons connected to him are gone… what are you going to do?"
Tamayo grew quiet for a moment. "I had planned to die in that fight," she said calmly. "To take Muzan down and join my family." She smiled faintly. "But now that I live… maybe I should spend the rest of my time atoning for my sins. I'll continue being a doctor and help more people."
Yushiro nodded without hesitation. "Wherever Tamayo-sama goes, I'll go too."
Akira smiled. "That's good. It's always better to live than to die."
After talking a bit longer, they finalized their plans. With their goodbyes said, Akira and Erika left Tamayo and Yushiro behind and began walking toward the Butterfly Mansion.
To deliver the medicine to Tanjiro.
They found Tanjiro lying in one of the patient beds, with Zenitsu and Inosuke resting in the beds beside him. Nezuko, Kanao, Aoi, and the three little girls stood nearby, watching over them.
Zenitsu and Inosuke were screaming loudly, just as usual.
"I DON'T WANNA TAKE MEDICINE!" Zenitsu wailed.
"I'LL BITE IT BACK!" Inosuke shouted, flailing his arms.
Despite the noise, neither of them was seriously injured. They had simply pushed themselves a bit too hard during the battle, so they were resting as a precaution.
When Tanjiro noticed Akira and Erika entering the room, his face immediately brightened. "Akira-san! Erika-san!"
Akira glanced around at the chaos and sighed lightly. "You guys are lively as usual."
Erika smiled and moved toward the girls. She had always gotten along well with them, and she quickly joined Nezuko. Even though Nezuko was human now, she still remembered the time they had spent together, so the two of them talked like close friends, asking how everyone was doing and what they planned to do next.
Meanwhile, Akira walked over to Tanjiro and handed him a small vial. "This is for you."
Zenitsu's head snapped toward them. "WHAT IS THAT?!" he yelled. "IS IT SOMETHING GOOD?! WHY IS TANJIRO THE ONLY ONE GETTING IT?!"
Inosuke immediately joined in. "YEAH! I WANT ONE TOO!"
Akira replied flatly, "It's not food. It's medicine."
Both of them instantly relaxed.
"Oh," Zenitsu said. "It's just medicine."
"Tch," Inosuke clicked his tongue. "That's boring."
Tanjiro accepted the vial without hesitation and drank it. He trusted Akira completely, especially after Nezuko had been turned human.
Soon, the medicine took effect.
However, the mark on Tanjiro's forehead didn't disappear.
Erika tilted her head slightly. "Did it… not work?"
Akira shook his head after a brief look. "No, I think it did work. His Mark is a permanent one, unlike the others; he always had it, I guess."
Tanjiro blinked. "Then… what does this medicine do anyway?"
Akira stared at him for a second. "You should have asked that before drinking it."
Then he explained calmly, "It reverses the damage caused by the Demon Slayer Mark and permanently locks it away. In other words, you'll have a normal lifespan."
Tanjiro absorbed that quietly. "I see… that's what it does."
Nezuko stepped forward, her expression soft and earnest. "Thank you, Akira-san. Not only did you turn me back into a human… You also helped my brother live a long life."
She had known about the Demon Slayer Mark. She had been afraid, terrified, that Tanjiro would die at twenty-five.
Now, that fear was gone.
Akira waved it off lightly. "I'm just doing what I want. Don't worry about it."
After talking for a bit longer, Tanjiro hesitated before finally asking,
"Akira-san… are you guys leaving?"
The room fell silent.
Akira nodded. "Yes. We'll be leaving soon."
They had all known this day would come. From the moment Akira and Erika appeared in their lives, they knew they would one day leave.
Even so, knowing it and hearing it aloud were very different things.
The sadness lingered quietly in the room.
One of the little girls tugged gently on Erika's sleeve.
"You're really going away?"
Erika knelt down to their level, meeting their eyes.
"Yeah," she said softly. "But I'll remember you. All of you."
The girls nodded, trying their best to be brave, then immediately wrapped their arms around her legs, clinging tightly.
Erika froze for a moment… then smiled and rested a hand on their heads, letting them hold on just a little longer.
Tanjiro looked up at Akira after a moment of silence.
"So… what will you do next?"
Akira thought for a second, then answered calmly,
"The demons are dead. But there are still so many things that need to be done. So many people need to be saved. And so many evils that still exist."
He smiled faintly, as if he were a hero going on an epic journey.
"So our journey has only just begun."
Tanjiro nodded slowly. "I see…"
Then, hesitating, he asked, "Will you ever come back?"
"Of course," Akira replied without hesitation. "We will, when we have time."
Erika nodded as well. "Right. When we have time, we'll definitely come back to meet everyone again. From time to time."
The atmosphere lightened immediately. Smiles appeared, and the heaviness in the room eased just a little.
Aoi tilted her head. "So… are you leaving right now?"
Akira shook his head. "No. We still have a few things to finish up."
Then he added, almost casually, "And I did promise to throw a huge feast for everyone, right?"
Inosuke's eyes lit up instantly.
"YEAH! FEAST! FOOD!"
The others laughed. Akira's cooking was already legendary among them, so the promise alone lifted everyone's spirits.
As they continued talking, a sudden flutter of wings sounded near the window.
Raven and Rose, their Kasugai crows, flew in and perched nearby.
"You are summoned!"
"The Hashira meeting is beginning!"
Akira let out a long sigh.
"…Well," he said, rubbing the back of his neck, "I guess this is the final Hashira meeting."