~# Thank You for 200 Powerstones, Here's Your Bonus Chapter!
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Butterfly Mansion Courtyard
Kaidō stood in the courtyard, staring up at the night sky, lost in thought.
'I got cocky. Having the system, having strength—I let it go to my head. Thought I was hot shit, ready to take on Upper Ranks. What a joke. Heh... I was naive. Arrogant. Became a Hashira and suddenly thought I could look down on Upper Ranks? Look how that turned out. I got too comfortable, too lazy. Started believing the system made me invincible. Pathetic.'
The fight with Upper Rank Two had been a brutal wake-up call. The power gap was enormous. He'd been delusional thinking that beating three Hashira in sparring meant he could challenge Upper Ranks. Even the weakest Upper Rank—Lower Six—required at least two Hashira working together to kill. The top three Upper Ranks? In a completely different league.
'Whatever. At least now I know what I need to do.'
'Been a while since I played the flute. Wonder if I'm rusty after being reincarnated.'
In his previous life, Kaidō had loved playing the flute. Whenever he was troubled, the music would calm his mind and center his thoughts.
He opened the System Lifestyle Shop, browsing for musical instruments.
"Wait, what's this?"
[White Flute: Carved from premium white gem. Smooth texture, pure white color.]
"Perfect. I'll take it." He spent 3,000 yen and willed the flute into existence. It materialized in his hands.
Raising it to his lips, he began to play.
A hauntingly beautiful melody drifted across the Demon Slayer Corps compound.
The three girls had noticed Kaidō missing from his room and assumed he'd wandered off again. Following the sound, they found him in the courtyard. Instead of interrupting, they quietly sat on the wooden platform and listened. Inside the infirmary, patients who'd been restless gradually calmed down.
Shinobu Kocho, kneeling before her sister Kanae's memorial, heard the melody. Her turbulent heart grew still—but tears streamed down her face. "Sister... I miss you so much."
Tengen Uzui, soaking in a hot spring with his three wives, paused. "Truly flamboyant, as expected!" He closed his eyes and listened.
Ubuyashiki Estate
"Missing his family, I suppose." Kagaya smiled gently, then turned to his wife and daughters. "I hope this moment of peace and tranquility can last forever. That no one else will have to leave us."
"It will," Amane Ubuyashiki assured him.
Hand in hand with his wife and daughters, Kagaya sat and listened to the flute's song.
Rengoku Estate
Shinjuro Rengoku, the former Flame Hashira, heard the melody and felt his heart grow strangely calm. But it only made him miss his late wife more. Ever since she'd passed, he'd spiraled into alcoholism, drowning his sorrows in sake. Even when his eldest son Kyojuro became a Hashira, Shinjuro had remained indifferent.
"Ruka... am I doing the right thing?" He took another long drink.
That night, the entire Demon Slayer Corps experienced a rare moment of peace.
...
Three Days Later
Kaidō had fully absorbed the Healing Pill's effects and recovered completely. But Aoi Kanzaki and the three girls insisted on one final checkup. Outnumbered, he relented.
"You're completely healed. No issues at all!" Aoi confirmed after the examination.
"Finally! Time to get back to training. I've been unconscious for three months and recovering for several more days. Any longer and I'll turn into deadweight."
'If I don't complete my quests, I'll never get home.' That thought remained unspoken.
"Do you need help with your training?"
"Nah, I'll handle it myself. You're already busy taking care of all these patients. Don't want to add to your workload."
"Alright. Just let us know if you need anything."
"Will do. Thanks, Aoi." He smiled warmly.
"N-no need to thank me! It's... it's my job!" Seeing his smile brought back memories from a few nights ago. Her face flushed bright red.
"Ah! Aoi-nee is blushing again!" the three girls chorused.
"I am not!" Aoi protested.
"CAW CAW! Master, I'm back!" Kuroha swooped through the window and landed on the sill.
"Kuroha! Long time no see, buddy." Kaidō scooped up the crow and gave him some well-deserved head scratches. He'd missed this.
"By the way, where's my greatsword?"
"While you were recovering, the Kakushi brought it to your estate," Aoi replied.
"Makes sense. Alright then, I'm heading out. I'll drop by again when I get the chance!"
"Goodbye, Dragon Hashira-sama! Play the flute for us next time!" the three girls called out.
"Sure."
"Oh, Insect Hashira-sama wanted me to tell you—once you're better, she needs to speak with you. She said it's important."
"Got it. Thanks. See you later!"
...
Kaidō pushed open the door to Shinobu's workspace. The room was packed with bottles, jars, vials, and test tubes lining every shelf. The air was thick with the sweet scent of wisteria.
"Shinobu-nee, you wanted to see me?"
"Oh my, you're here, little Kaidō! Come, sit!" Shinobu stopped working on her latest poison concoction and gestured to the chair beside her.
"I'm not little! I'm perfectly normal-sized!" Kaidō protested.
"But you look pretty small!" Shinobu leaned closer, her face mere centimeters from his.
Kaidō's face turned crimson. Steam practically rose from his head like a boiling kettle.
Satisfied with her teasing, Shinobu pulled back with a giggle. "Alright, alright. Let's talk business. I actually have two things I want to ask you..."
"You want to know about the Upper Rank I fought and about the pill I gave the Master, right?"
"How did you know?"
"I've heard your sister was killed by an Upper Rank who uses ice-based Blood Demon Arts. You're desperate for intel on that demon so you can get revenge. As for the pill—you want to analyze its components. If you can replicate it, it could be invaluable for the Corps when we eventually face Muzan. Am I right, Shinobu-nee?"
"Yes. I will kill that demon with my own hands. For my sister."
"Shinobu-nee... do you trust me?"
"Why do you ask?"
"If you trust me, then please—stay alive. Stop ingesting wisteria poison. You want to witness your enemy's death personally, don't you?"
Shinobu studied his eyes for a long moment. For reasons she couldn't quite explain, she chose to believe him. Though just to be safe, she'd keep her backup plan in motion.
"Alright. I trust you."
Kaidō smiled. He knew Shinobu would probably continue ingesting the poison anyway, but at least this was a start.
"Here—a Longevity Pill. Study it. Hope it helps." He pretended to fish it from his pocket while actually pulling it from his system inventory. He'd given one to Kagaya, used one after the Doma fight. Ten remained. He'd planned to save them for the Infinity Castle battle to counteract the Demon Slayer Mark's side effects for the other Hashira. But one now, nine later—still plenty.
"Thank you."
"Don't mention it."
...
Back at His Estate
Kaidō browsed the System Lifestyle Shop for training equipment.
"Dumbbells—useful. Bought."
"Leg weights—perfect for speed training. Bought."
"Sandbags—can use them for wrist strength or weighted running. Bought."
"Might as well grab some snacks too. I'll give them to Aoi and the girls later as thanks for taking care of me."
"System, can you ship these the normal way instead of materializing them out of thin air? That would look weird."
[Affirmative.]
...
"Kaidō-sama, several packages arrived for you."
"Thanks for bringing them."
"Not at all—it's our duty!"
'That was fast. Classic system efficiency.'
[Ding! New Quest Available.]
[Quest: Intensive Training]
[Complete daily: 3,000-meter weighted run, 1,000 push-ups, 1,000 sword swings. Duration: Three months.]
[Rewards: Sonic Speed Pill x1, Agility Pill x1, Enhanced Tiger-Dragon Pill x1, Random Interdimensional Energy 5-10%]
[Sonic Speed Pill: Permanently increases movement speed.]
[Agility Pill: Permanently increases reflexes and dexterity.]
[Enhanced Tiger-Dragon Pill: System-modified version. Strengthens body, increases muscle density and physical toughness, tempers flesh and bone.]
"Perfect timing. Training plus rewards—can't beat that."
He strapped on the weighted vest, secured the leg weights, and began running laps around Corps Headquarters.
...
Three Months Later
[Ding! Quest Complete.]
[Rewards: Sonic Speed Pill x1, Agility Pill x1, Enhanced Tiger-Dragon Pill x1, Interdimensional Energy +5%]
[Current Interdimensional Energy: 60%]
'More than halfway there. Almost home.' The milestone filled him with genuine happiness. Then he examined the quest rewards and items he'd drawn randomly over the past three months.
[Berserk Pill: Grants berserk state for three hours. Strength increases threefold. After effect ends, user enters weakened state.]
[Sticky Bombs: Extremely adhesive with high explosive power.]
[Time Hourglass (Single Use): Rewinds target's time flow to their state ten minutes prior.]
'Berserk Pill—great boost but harsh side effects. Emergency use only. Sticky Bombs... am I supposed to stick these to Muzan's ass and blow him up? Whatever, might come in handy eventually. Time Hourglass—limited to ten minutes, but used right, it could turn the tide in critical moments.'
Overall, pretty satisfied with his haul.
He swallowed the Enhanced Tiger-Dragon Pill. Immediately, it felt like his entire body was being roasted over lava while his blood boiled. Simultaneously, it was as if someone was repeatedly breaking and resetting every bone in his body.
"Ngh! This sucks! Should've taken the other pills first!"
The agony lasted ten minutes. But when it ended, Kaidō could feel the fundamental transformation his body had undergone.
"Now this is what I'm talking about! Heh... Doma, just you wait. One day I'm settling that score!"
He downed the Sonic Speed Pill and Agility Pill as well.
...
After finishing his training regimen, Kaidō returned to his patrol zone. He also started clearing demons from Obanai's territory—which wasn't that far from his own.
Obanai was bewildered. 'You cleared out all the demons in my zone. What am I supposed to do now?'
Kaidō's response was simple: "Mitsuri's been swamped. Don't you want to lighten her load?"
Obanai felt like something was off about that logic, but he couldn't quite put his finger on what. He decided to let it go and head back to Headquarters instead.
Then Kaidō's next comment made him reconsider.
"My patrol zone's been such a pain lately. Just when I clear out a bunch of demons, more show up. Wonder if anyone wants to trade zones? I heard Mitsuri's territory is closest to mine..." Kaidō said this casually, as if talking to himself.
"I'll trade with you! If you're finding it troublesome, I'll handle it. I love hunting demons anyway!" Obanai's answer came immediately. Inside, he was ecstatic. 'Closest to Mitsuri's zone? After patrol, I can visit her!'
"Deal! Head over whenever. Your zone is mine now. No backing out!"
"I won't. And you better not either."
Obanai started to leave, then paused and looked back. "Thanks."
Kaidō grinned. "If you really wanna thank me, treat me to kelp strips!"
"Done."
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