After finishing their barbecue, Hiru and Yoriichi returned to the Wisteria House, only to be intercepted by a Kakushi .
"Human Hashira, you have a letter."
"A letter for me?" Hiru took the envelope the Kakushi handed him, opening it with a puzzled look. "I don't know many people... who could be writing to me?"
Yoriichi followed behind Hiru. "Looks like you've made friends too, Hiru."
"Hardly... It's a letter from the Master." Hiru shook the paper. "Time to change his medicine soon."
"Are you sure your medicine is safe, Hiru..." Though masked, Yoriichi's voice clearly wavered. "You once made me sick for three whole days..."
Hiru: "...That was a mistake! A mistake! And my medicine is harmless to humans except for a few specific cases!"
"If possible, maybe we should consult Miss Tamayo..."
"Trust me on this once in a while!"
"But..."
"No buts!" Hiru turned around and pushed Yoriichi toward the exit. "I'll handle things here! You go take care of your duties, big brother!"
Yoriichi could only shake his head helplessly. "Alright... I understand. But please be cautious. The Master is crucial to the Demon Slayer Corps."
"I—know—that—"
Yoriichi reached up to ruffle Hiru's hair again. "If you're in danger, don't hesitate, okay?"
"Yeah, next time I'll definitely notify you first."
"Then I'll be going." Yoriichi glanced at the surrounding Kakushi and gave a slight nod. "Please look after my brother."
"Yes, Sun Hashira-sama!"
"Leave it to us!"
"We'll accomplish the mission!"
"Who's looking after whom is still up in the air..." Hiru muttered. "But I need to write a reply first... Could you fetch me some paper and ink?"
"Certainly! Delivered to your room immediately!"
Hiru watched the group of Kakushi who, energized as if by a shot of Yoriichi's request, practically vibrated with enthusiasm. He twitched his lips, finding it hard to comprehend.
After writing his reply, Hiru stayed for three more days. Once he obtained the medicine from Tamayo, he summoned a Kasugai Crow and headed for the Demon Slayer Corps Headquarters. Guided by Kakushi, he also met with Ubuyashiki Kagaya.
The first words Hiru exchanged with Ubuyashiki Kagaya were: "Your health is far worse than I imagined."
Ubuyashiki Kagaya maintained his unchanging gentle expression. "Thank you for your concern."
Hiru stepped directly before him, crouching to take his pulse. "Hallucinations?"
"Yes."
"What about the rest of your body? Any abnormalities?"
"None. If anything, my body feels much lighter." Ubuyashiki Kagaya shook his head, a hint of curiosity in his eyes. "But the medicines you prescribed seem rather uncommon. Do you have a formula?"
"Mm. They're failed experiments from my research on human-transforming drugs. Harmless to humans, yet precise in killing demon cells." Hiru withdrew his hand. "Looks like you've been following your doctor's orders diligently. Keep taking them for two more days, and the organs fused with your Blood Demon Art should be eliminated."
Ubuyashiki Kagaya: ...You're saying terrifying things with a completely calm expression.
"How did you determine the dosage timing?"
"Because I tested them all on myself. I nearly died several times, so I know the side effects and effects inside out."
Ubuyashiki Kagaya: ...?
"Then..."
"Don't ask." Hiru raised a hand to cut off the question. "I don't want to remember."
Ubuyashiki Kagaya once again silently clutched his stomach.
"Stomachache again? You really should watch what you eat." Hiru lifted his head. "By the way, was the person who prescribed your medicine before part of the Demon Slayer Corps? I'll go talk to them and get you a new prescription. Having them involved would make things easier for me too."
Ubuyashiki Kagaya sighed. "At this hour... Reima should be at the pharmaceutical workshop."
"Ah, right. This time out, I sort of ran into Muzan head-on. And for certain reasons, he'll likely try every trick to track me down," Hiru said as he stood up. "So from now on, I'll only come here for the Hashira Meeting. For your own safety, don't contact me unless absolutely necessary. That's all. Get some rest."
Watching Hiru leave without hesitation, Ubuyashiki Kagaya sat clutching his stomach for a long while before lowering his hand.
"...He never fails to deliver shocking news."
...
When Hiru arrived at the pharmaceutical lab, Mikazuki Reima was instructing the young girl named Shinobu in swordsmanship.
Hiru stood nearby, waiting for them to finish.
But the longer he watched, the more he couldn't help but frown. The reason was simple—Shinobu's strength was too weak. So weak she couldn't even cleanly sever the training dummy with her iron blade.
While age played a factor, given Shinobu's current growth rate...
"That's enough for today," Reima said, frowning. "Shinobu, I'll say it again: at your current level, you won't be able to sever a demon's neck. Continuing like this, becoming a Swordsman would be nothing but suicide."
"I can kill demons!"
"Don't be ridiculous. If you can't even cut through a neck, how do you expect to kill a demon?" Hiru stepped forward. "Demons won't show you mercy."
Shinobu puffed out her cheeks. "I'll use medicine!"
"Applying it to your blade won't be enough to kill a demon," Hiru said, looking down at her and unable to resist poking her plump cheeks. "Besides, demons aren't going to just eat your medicine..."
"I won't give up, no matter what! I refuse to forgive any demon!" Shinobu glared stubbornly at Hiru. "If one strike doesn't work, I'll strike ten times. If ten times aren't enough, I'll strike a hundred! I absolutely, absolutely won't let a single demon off the hook!"
"Then how about begging me?" Hiru chuckled, bending down close to Shinobu. "I'm quite skilled at mixing potions, you know?"
But Shinobu just stuck out her tongue, spat, and went back to tending the medicinal garden, completely ignoring Hiru's words.
"What? I'm serious, you know—"
"I'll explain your medical skills to this child in detail later," Mikazuki Reima chuckled. "Oh, and congratulations on becoming a Hashira."
"Nothing to congratulate," Hiru waved it off. "I came to ask about the Master's regular medications and his physical condition."
"The Master's health improved significantly after you treated him, and the curse's corrosion weakened. I'm truly grateful." Mikazuki wore a wistful expression. "I've always been concerned about the Master's health and sought to treat him, but these past years have yielded no results whatsoever. You're far more skilled than I ever was."
"It's simply a matter of specialization. That wasn't a curse at all—it was the erosion of Blood Demon Arts. Treating it like an ordinary illness was bound to fail."
"Blood Demon Art corruption?" Mikazuki visibly froze. "Could you elaborate?"
"That's precisely why I came to you. Due to certain matters, I won't be able to visit often except for the Hashira Meeting. This task must be entrusted to you." Hiru tilted his chin. "Let's discuss this inside."
"Understood." Mikazuki didn't press for reasons, simply following Hiru into the house.
After their discussion, Hiru also handed over all his failed formulas—those harmless to humans—to Mikazuki. He instructed him to thoroughly study the recipes and later pass them on to Kakushi .
"As for Shinobu, let her confirm her combat style first. Once that's settled, you can decide whether to teach her the formulas. Otherwise, with her current strength..." Hiru sighed. "I'm quite certain she'd just be delivering herself to her doom."
Mikazuki smiled. "Then I'll thank her for you in advance."
"Honestly, I'd rather receive her thanks personally," Hiru chuckled. "Speaking of which, the Mount Fujikasane assessment is approaching soon. Will Shinobu participate?"
"I plan to have her take it next year," Mikazuki shook his head. "She's still too impulsive. If she can't calm her mind, facing a demon will only lead to certain death."
"Next year is way too soon, isn't it? How old is she?"
"Eleven."
Hiru: ...Seriously? I surpassed that height at nine. Aren't girls supposed to develop faster?
"That's been my biggest headache..." Mikazuki clearly understood Hiru's shock. "Besides, the current Breathing Styles aren't suitable for Shinobu either.
"The Rock, Thunder, and Wind Breathing Styles are too physically demanding, and Shinobu doesn't have the potential for the Flame Breath... Her Water Breath isn't smooth either. I've tried teaching her other derivative breathing techniques too, but Shinobu's strength is simply too weak. While her explosive power is good, clearly defeating demons isn't something that can be done with explosive power alone.
"If she still hasn't adapted to fighting with Breathing Styles by next year, I'll consider advising her to join the Kakushi Corps."
"True, physical strength is an insurmountable barrier," Hiru nodded. "After all, if you're strong enough, you can simply smash a demon to pieces to kill it."
Mikazuki Reima: "...Actually, I've been meaning to ask."
"Hm? What is it?"
"What exactly did Hiru do to the demons before joining the Demon Slayer Corps?" Mikazuki covered the lower half of his face with his remaining arm, his expression hard to read. "You have far too much unnecessary, in-depth knowledge about them."
Hiru: ...How am I supposed to respond to that?
Fortunately, Shinobu entered carrying a letter and presented it to Hiru with both hands. "A letter for you, Human Hashira."
"So now they know I'm a Human Hashira..." Hiru muttered as he took the letter. His expression instantly turned disdainful after reading it. "I hate babysitting."
"What's wrong?"
"The lord wants me to oversee this year's Mount Fujikasane assessment," Hiru passed the letter to Mikazuki. "He's worried last year's incident might repeat."
"Last year was indeed perilous. Thankfully you and your brother were there." Mikazuki took the letter. "That guy Urokodaki must be feeling pretty rough knowing about it."
"Why?"
"Because that demon was captured by Urokodaki himself. I even escorted it here with him back then." After reading, Mikazuki returned the letter and sighed. "I wonder if there are enough demons in Mount Fujikasane for this year's exam..."
"Aren't demons pretty easy to catch?" Hiru stroked his chin. "I caught nearly forty of them. Even if others are slower, they should be able to gather a similar number, right?"
"...Hiru, you really lack common sense." Mikazuki looked utterly exasperated. "Most Demon Slayer Corps swordsmen only manage to capture this many demons in an entire year.
"You know how regenerative demons are. The moment they recover, they start clamoring to devour people. So even with the wisteria's aid, it's often difficult for the Kakushis to safely transport them to Mount Fujikasane.
"Your success was entirely due to the Bright Red Nichirin Sword suppressing their regenerative abilities. Without it, your tally would've been halved. But thanks to you, this year's assessment difficulty is no longer an issue. With you overseeing things, we shouldn't see any unexpected casualties."
"I just think it's such a hassle..."
Mikazuki hooked his single arm around Hiru's shoulder. "If you go early, you might even snag a promising stepson."
"I don't even know the Breathing Styles—what could I possibly teach them?"
"Where there's a will, there's a way—youngsters shouldn't be so unenthusiastic!"
"..."
Despite his deep distaste for the job, Hiru headed to Mount Fujikasane as requested, bringing along the twin daughters of Ubuyashiki Kagaya—Ubuyashiki Hinaki and Ubuyashiki Nichika.
Both sported short white hair and cat-like eyes. They carried themselves with proper decorum and spoke with remarkable synchronicity. Were it not for their differently colored hair ribbons, outsiders would struggle to tell the identical twins apart.
Last year as well, they had been the ones to receive the many Swordsmen who came to Mount Fujikasane for their evaluations.
"Mount Fujikasane is just as beautiful as ever." Hiru gently lifted a drooping wisteria with his fingertips, glancing at the little twins following behind him. "What happens next? Should I wait here with you?"
"We're grateful you escorted us all the way here."
"Please proceed to the rest hut halfway up the mountain."
"Everything has been arranged by Kakushi."
"We will handle the assessment."
"Should any special circumstances arise, we will notify you promptly."
"Consider this a vacation."
"What kind of vacation requires constant standby…" Hiru's lips twitched. "And could you please stop speaking like that? It's creepy."
The two exchanged a glance, bowed together, and spoke in unison. "We sincerely apologize for making you uncomfortable."
Hiru: ...Even creepier.
"Anyway, I'll go with you to the platform first." Hiru turned his gaze forward again. "I'll rest after seeing everyone off."
"Thank you very much." the twins said together again.
Hiru silently quickened his pace.