The Butterfly Mansion.
A week had passed since Uzui Tengen activated his Demon Slayer Mark and left.
The minor injuries on Tanjirou and the others had long since disappeared under Kochou Shinobu's exquisite treatment, leaving no scars behind.
"Mizuki, Miss Tamayo asked you to go see her when you have time," Kochou Shinobu said, returning from outside the Butterfly Mansion.
Watching the group forcing Zenitsu into frantic training in the courtyard, Mizuki paused, then turned her head and asked, "Tamayo? Did she say what it was about?"
Kochou Shinobu shook her head: "She didn't mention it."
"I understand." Mizuki nodded lightly, stood up, and said, "Then I'll head out for a bit."
The sun was about to set, which was the time for demons to emerge.
Mizuki didn't greet Tanjirou and the others but left the Butterfly Mansion directly... Because Tamayo needed to treat Yae's father, Ubuyashiki had arranged for her to stay in a corner of the headquarters.
Ubuyashiki was unaware that Muzan possessed the ability to roughly locate demons, but his caution allowed the Demon Slayer Corps headquarters to remain safe.
Arriving at Tamayo and the others' residence, Ubuyashiki had directly built a luxurious mansion here since Tamayo was responsible for research, and he sent a large number of medical instruments and related items to her.
The logistical support work was handled extremely well.
The street in front of the mansion was deserted, with no sign of human presence.
Even members of the Demon Slayer Corps rarely came here.
The night was hazy, having just fallen.
Mizuki tried knocking on the door and waited for a moment.
Creak~
The door opened, and Yushiro, looking like a young boy, appeared before her.
Yushiro stepped aside: "It's you. Lady Tamayo has been waiting for a long time."
Ever since Mizuki said, 'If you keep throwing childish tantrums, girls won't like you,' in front of Yushiro last time.
Yushiro had completely changed. He was no longer reckless and irritable in front of them like before.
He had become steady, fitting his apparent age.
"Excuse me for intruding." Mizuki nodded slightly and followed Yushiro into the mansion.
I have to say, the Ubuyashiki Clan is truly generous.
They just gave away such a luxurious house.
Wait... why did Tamayo get a house when she defected as a demon, but she didn't?
Is this the difference in treatment between high-tech personnel and security personnel?
Mizuki felt a little resentful.
That's too much!
Yushiro shivered, feeling as if there was something unclean nearby.
Walking a bit further, Mizuki saw Yae helping an elderly man with short, graying hair stroll along the gravel path under the moonlight.
"Ah, it's Miss Mizuki!" Yae also noticed the two of them and tugged at the person beside her, "Dad! It's Miss Mizuki!"
Mizuki had visited before, but at that time, Yae's father had not fully recovered.
Transforming a human into a demon was not a simple matter, and even with the successful example of Yushiro, it still took Tamayo a considerable amount of time.
Yae's father was a kind old man. Having long heard from his daughter that Mizuki had protected him from the Demon Slayers, he respectfully attempted to kneel before Mizuki from a distance.
Mizuki disliked this kind of formality the most, but unfortunately, it was how others expressed their gratitude.
Having spent some time here, Mizuki wiped the cold sweat from her forehead and bid farewell to the two.
Along the way, Yushiro actually wasn't impatient at all.
If it were before, he would definitely have said something like this.
'How long are you women going to talk?! How long do you plan to make Lady Tamayo wait?'
He's making progress.
Arriving at Tamayo's pharmacy, Mizuki could smell a mixture of medicinal herbs from a distance.
Yushiro knocked on the door and pushed it open: "Lady Tamayo, she's here."
Tamayo was sitting in front of a microscope observing something. Hearing the voice, she turned and smiled gently: "Mizuki, you've arrived."
Ah, Lady Tamayo's smiling face~
Stars twinkled in Yushiro's eyes.
Although it wasn't directed at him... Yushiro bowed slightly, backed out of the room, and closed the door, leaving the space to the two of them.
"I heard from Shinobu that you needed to see me?" Mizuki nodded, made herself comfortable, and sat down on a stool.
Tamayo rummaged through a drawer, then came over to her: "Well, let's leave that aside for now. Hold out your arm."
"Wh-" Mizuki stopped mid-sentence, feeling her scalp prickle at the sight of the needle in Tamayo's hand.
Mizuki's face went pale: "Can you pretend I was never here?"
"What do you think, Mizuki?"
"...I think it's possible."
However, Tamayo completely ignored her reluctance, pressed her arm onto the table, and drew a large syringe full of blood.
Mizuki lay weakly slumped on the table.
She realized she wasn't actually afraid of needles; she had simply been traumatized by Tamayo.
Mizuki simply buried her head under the table, giving up resistance.
But after waiting for a while and not feeling a second prick, she couldn't help but look up in confusion.
"Are you not drawing more?"
Tamayo returned to the microscope, observing something unknown.
Hearing this, Tamayo turned her head in surprise: "Mizuki, do you want more blood drawn?"
Mizuki quickly shook her head: "No, no, I don't!"
Tamayo put her eye back to the microscope and said, "Speaking of which, how much do you know about your own Blood Demon Art, Mizuki?"
"Blood Demon Art?" Mizuki was stunned, pondered for a moment, and said, "As a demon, isn't a Blood Demon Art just an innate ability?"
"My Blood Demon Art is, of course, the ability to repair the human body and amplify the power of sword energy..."
She had originally planned to use the effect of amplifying sword energy power on others, but she later discovered something.
Because her blood temperature was too low, applying it to a Nichirin Blade would prevent the scarlet blade from activating normally.
Compared to range and power, it was obvious that her blood's amplification in this regard was inferior to the scarlet blade, which could suppress demon regeneration and cause intense pain.
This caused the ability to become somewhat useless; it couldn't be effective against demons, and might even backfire when facing strong enemies.
Tamayo suddenly murmured, "Just as I thought..."
"Hm?"
"Your blood temperature has dropped again compared to the last time I drew it."
"Temperature?"
"Don't you understand?" Tamayo thought for a moment and explained, "The current temperature of your blood is around minus seventy degrees Celsius."
"The last time I drew your blood, the temperature was clearly still around minus twenty degrees Celsius."
Mizuki raised an eyebrow: "But shouldn't such a low temperature cause it to freeze?"
Although she had mostly forgotten her knowledge and hadn't used her brain much over the years, she couldn't imagine minus seventy degrees still being liquid.
Moreover... she couldn't help but cut a small slit on her palm and smear the blood onto the back of her hand: "It doesn't feel very cold, though?"
Tamayo: "..."
Tamayo said helplessly, "Using yourself as a reference point is meaningless. You should try it on someone else."
"Furthermore, demons are not beings that can be judged by common sense; they cannot be viewed purely from an ordinary perspective."
Mizuki didn't quite understand and scratched her head: "So, is this a bad thing?"
"...It's hard to say right now..." Tamayo hesitated for a moment, then added, "But I don't think it's a bad thing."
"Just now, I mixed your blood with mine. Do you know what happened?"
"They merged?"
"...Cells. The regeneration speed of my blood cells slowed down." A vein throbbed on Tamayo's forehead.
How did a perfectly normal person turn into an idiot after two hundred years?
Mizuki finally understood: "Slower regeneration speed?"
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