Chapter 40: Butterfly Kanae

Day after day, year after year.

Time slipped away swiftly.

It had been nearly two years since Zero joined the Demon Slayer Corps.

On this day, after concluding the third round of examinations at Mount Fujibayashi as examiner, Zero led everyone back to the Demon Slayer Corps headquarters.

The results of this session were decent: out of twenty candidates, half passed the exam and officially became Demon Slayer swordsmen.

Half of them were swordsmen who had failed in the previous session and reapplied.

Back at headquarters, with no missions pending,

With nothing to do, Zero returned to his residence, entered his room, sat at the desk, and began writing his diary:

【December 8, morning, weather: the sky is sleeping in】

It has been two years since I joined the Demon Slayer Corps; I have supervised three rounds of the Fujibayashi Mountain examinations.

【These two years, I’ve either been killing demons or on the way to kill them! Those demons who shirk their duties and run at the sight of me are utterly useless…】

After finishing his diary, just as he was about to close the book and rest, he noticed the date—and something stirred in his memory…

“December 8… hmm… I remember—Kanae’s birthday is today, isn’t it?”

He recalled meeting the Butterfly sisters for the first time—Kanae had recommended him to join the Demon Slayer Corps.

Back then, he barely understood this world and had been wary of them, but over time, he realized the sisters were truly kind.

Moreover, most members of the Demon Slayer Corps were the same—though their personalities differed, overall, they were all good people.

“I didn’t realize it had already been two years since I joined. I wonder how Luo Li and No.1 and the others are doing out there under the stars?… Never mind, I won’t think about that now. Since today is Kanae’s birthday, I’ll prepare a surprise for her!”

Just as he was about to act, he felt his leg being hugged—he looked down and saw the child, Rokutai.

He must have entered while Zero’s door was left open when he returned to his room.

And since Zero was writing his diary, he hadn’t noticed Rokutai’s arrival.

“Zero-nii… hug…” Rokutai had grown a bit, but was still a child, so his speech was still a little clumsy.

Zero smiled faintly, picked him up, and pinched his tiny cheek gently: “You, always wanting hugs from me.”

Rokutai loved being held by Zero—not only because of Zero’s natural body scent, but because he felt safe in his arms.

“Sorry, Zero, I just woke up and didn’t notice Rokutai was gone—I was so worried!” Kamado Koyuki, having risen, found Rokutai missing and rushed over.

She searched everywhere, and when she saw Zero’s door open, she hurried over in a panic.

Her hair was disheveled, she wore her nightgown, looking slightly lazy, and with the beauty mark beside her lip, she resembled a gentle neighborly older sister.

With their lives improved, the Kamado family lived comfortably here, and Kamado Koyuki often kept the residence neatly organized.

Zero had told her not to work so hard every day—occasional rest was fine.

So today, she and the children slept a little longer.

When Zero returned, they were still asleep.

He didn’t disturb them, quietly slipping back to his own room.

As for Xiao Yue, she had been taken by Kanae to the Butterfly House to play…

“It’s fine, Aunt Koyuki, you and the children rest more today. I have no missions now; taking care of Rokutai is no trouble.”

“Th-then… alright. I’m sorry to trouble you.”

“We’re family—no trouble at all.”

“Yes, we’re family… I hope Tanjiro’s little sister recovers soon.” As Kamado Koyuki spoke these words, her gaze at Zero carried an unspoken meaning—she looked satisfied.

“Huh… I must be imagining things… it must be… no, it’s definitely my illusion!” Zero thought to himself.

…

Near noon, Zero found several members of the “Hidden” unit and asked them to purchase ingredients for making a cake, instructing them to return before dinner—urgent use.

If he was to give Kanae a surprise, doing it himself was best.

Though the Hidden members didn’t understand why, since it was a request from a Pillar—especially Zero, the Zero Pillar—they moved at once.

Then Zero went inside and told Kamado Koyuki his plan—to give his friend a birthday surprise—and asked for her help.

Kamado Koyuki agreed without hesitation; Zero had saved her family, so this small favor was nothing.

Takeo and Shigeru helped under Koyuki’s direction; Hana was assigned to watch over Rokutai.

“Master, I’m back~” Zero heard Xiao Yue’s voice outside as he prepared to work.

He turned and saw Xiao Yue fly straight into his arms, clinging to his chest.

He lifted her gently in his hands and sighed with a smile: “You, still acting like a child, even now.”

“Hehe~”

“Xiao Yue, today is Kanae’s birthday. I want to surprise her—after all, she helped us once. Can you keep Kanae and Shinobu away from here? I’ll have Snow notify you tonight, then you bring them over.”

“Mm-hmm, okay~ But can you take me out again tomorrow?”

“Of course. That’s always been my promise to you.”

“Great, it’s settled then!”

Watching Xiao Yue leave, Kamado Koyuki spoke: “You two siblings have such a close bond.”

“Yes. She’s been with me all this time—no matter what I do, she supports me unconditionally…” As he spoke, Zero realized something—he didn’t know when Xiao Yue had developed self-awareness.

He vaguely remembered that when he first created T0 (Xiao Yue), she had no such awareness—she simply followed orders without question…

But T0’s self-awareness seemed to have emerged…

“Master, I am T0. You are my creator.”

“Master, T0 requests to stay by your side forever…”

“Master, T0 is just a robot, but I want… I want to stay with you like Sister Luo Li…”

“T0… will always support you, no matter what…”

“When did these memories come from?” Zero’s eyes dimmed for a moment, lost in recollection—but he couldn’t recall how they had formed…

Only after Kamado Koyuki called his name several times did he snap back.

“Zero? Are you alright? Are you unwell? Why don’t you rest? I’ll handle the rest.”

“Ah… oh, I’m fine. Just remembered something.”

“Are you sure?” Kamado Koyuki still looked worried, reaching out to touch Zero’s forehead.

That gesture suddenly felt familiar to Zero—warm, comforting, as if he’d felt it before…

“Aunt Koyuki, I’m truly fine. Let’s not talk about it—let’s get these ingredients ready, we’ve got a lot to do.”

“Alright, I’ll follow your lead.”

…

Hours later, the Hidden unit completed Zero’s request, purchasing the cake ingredients. Though slightly late, to Zero, it was no issue.

Fortunately, his [Nanospace] contained some cake-making tools—mixers, whisks—all of which helped shorten preparation time, though he didn’t know why those tools were there.

Bringing the ingredients to the kitchen, he retrieved the tools from his [Nanospace]: eggbeater, mixer—items Kamado Koyuki had never seen. She covered her mouth in disbelief, staring at Zero.

Fortunately, he had previously organized his [Nanospace], categorizing all equipment and daily items—otherwise, finding them would have taken much longer.

“Aunt Koyuki, let me show you how to use this. First, separate the egg whites and yolks into these two large bowls, then use this eggbeater…”

…

Butterfly House.

Upon hearing Zero had returned, Kanae finished her duties at the Butterfly House and wished to visit him—but Xiao Yue kept blocking her.

Xiao Yue remembered her master’s task: prevent Kanae and Shinobu from going to the residence—this was a surprise.

If the surprise was discovered, it wouldn’t be a surprise.

“Xiao Yue, why can’t I go see Zero? Are you hiding something from me?” Kanae smiled gently, watching Xiao Yue’s eyes for clues.

“No reason! Don’t ask, Kanae! The Master has important business—he’ll be disturbed if you go now!”

Shinobu sensed something was off, but couldn’t pinpoint what—she felt helpless.

Kanae guessed: if Xiao Yue said Zero had important business, it must be serious.

Possibly related to Upper Moons or Muzan.

He was probably organizing intelligence.

So she stopped insisting.

“Alright, when can I see Zero?” Since she couldn’t go now, she’d wait until he finished—surely he wouldn’t be busy all day?

“Hmm… probably tonight. The Sound Carrier will notify me. Don’t worry, Kanae!”

Believing Xiao Yue, Kanae calmed down and, with nothing else to do, began arranging flowers in her room.

But Shinobu thought differently—she noticed her sister’s change: Kanae now seemed constantly attentive to Zero’s every movement.

Hearing news of Zero made her happier than anyone else—this sparked a thought: Could her sister truly have fallen for Zero?

Shinobu could see that in Zero’s eyes, the sisters were merely close friends—perhaps even treated like little sisters.

Over the past two years, Zero rarely returned to the Corps—coming back only once every one or two months to share gathered intelligence.

His presence had significantly reduced the Corps’ casualties.

Moreover, each time he returned, he brought many medicinal herbs to the Butterfly House—for emergencies…

Shinobu was glad her sister had found someone she loved—but a quiet sense of loss stirred within her, as if something had slipped away…

…

Nightfall.

After hours of work, the cake was finally finished.

Kamado Koyuki had prepared a full table of dishes; Takeo and Shigeru, who had helped, stared at the food, tears streaming from the corners of their mouths.

Seeing all preparations complete, Zero summoned his messenger crow, Snow, to notify Xiao Yue, the Ubuyashiki family of seven, and the other eleven Pillars (including the former Flame Pillar).

The Pillars were all at the Demon Slayer Corps headquarters precisely because of what Zero and Shinobu Michiru had done…

Upon receiving the crow’s message, they were puzzled—why had Zero summoned them to his residence?

But since they had come anyway, why not go see? They had no missions for now, and it was quiet—perfect for a visit to Zero’s house.

When they saw the Ubuyashiki family of seven also present, their confusion deepened.

Shinobu Shino: “The Master himself is here—this must mean something important.”

“Probably,” even Shinobu Kanae was unsure why Zero had gathered everyone.

Entering the residence and seeing its interior decor, they were even more astonished—aside from the Shinobu sisters, none of them had ever visited Zero’s home before.

He never imagined his residence could be so magnificent!

Uzui Tengen: “Absolutely splendid!”

Shinobu Michiru: “Tch, Zero really knows how to live.”

Rengoku Kyojuro: "Wu! This is great—I love the atmosphere, hahaha!"

Tokito Muichiro: “What’s hanging from the ceiling?”

“Everyone, welcome. I called you here not only to express my gratitude, but also because this concerns Shinobu Kanae.”

Hearing this, everyone grew more curious, their gazes turning to Shinobu Kanae.

Shinobu Kanae herself looked puzzled—why had Zero said that?

“Huh? Zero, what do you mean it concerns my sister?”

Zero only smiled faintly and said nothing.

“Please, take your seats.”

The Kamado family of five, the eleven Pillars, the Ubuyashiki family of seven, Uzui Tengen’s three wives—Maki, Hina, and Suma—and Rengoku Kyojuro’s sons, Rengoku Kyojuro and Rengoku Senjuro.

Fortunately, there were enough tables and the room was large enough!

Otherwise, it would never have held so many people!

“Zero, you said it’s about my sister—what is it?” Shinobu Shino asked anxiously.

“Today is your sister’s birthday. You were the ones who introduced me to the Demon Slayer Corps. So, besides thanking you, I wanted to celebrate Kanae’s birthday—it’s my small gesture.”

Everyone finally understood, except Shinobu Michiru, who fell silent—he had forgotten Shinobu Kanae’s birthday, but Zero remembered.

Zero raised his cup and said: “Everyone, may we destroy Muzan Kibutsuji soon. And happy birthday, Shinobu Kanae!”

Xiao Yue, perched on Zero’s shoulder, echoed: “Happy birthday, little Kanae~”

Shinobu Kanae’s eyes instantly filled with tears. Since her parents were killed by demons, she had lived with Shino, never once thought of celebrating her birthday.

Yet Zero remembered. She couldn’t even recall when she’d last celebrated.

“Kanae, my child, happy birthday!”

“Kanae-chan, happy birthday!”

“Sister, happy birthday!”…

Everyone offered their wishes, celebrating Shinobu Kanae’s birthday.

Uzui Tengen’s three wives, watching this warm scene, were filled with envy.

Kanroji Mitsuri’s eyes sparkled as she thought: “I wonder if Mr. Zero even knows my birthday?”

…

After the delicious meal, Zero carried out a three-tiered cake from the kitchen and placed it on the table.

The pink cake was coated thickly with cream on each layer, topped with a strawberry carved into a heart shape.

He cut the top layer for Shinobu Kanae and divided the remaining two layers into dozens of portions, ensuring everyone got a piece.

“Oh my, such a sweet, soft cake—thank you, Zero. This is the happiest birthday I’ve ever had!”

“This is for you! Happy birthday!”

Zero handed Shinobu Kanae a beautifully wrapped box.

She opened it: a delicate bracelet, composed of pale blue and gray-white beads, with a tiny silver butterfly hanging at the clasp.

“I’m sorry—it’s something I’ve carried with me for a long time, but it’s still new. I hope you don’t mind…” Before he finished, Shinobu Kanae embraced him tightly.

“This bracelet is beautiful—I love it. Thank you, Zero.”

Everyone watching them forgot to eat their cake.

Uzui Tengen’s three wives stared with envy.

Maki: “Wow~ So sweet~”

Hina: “I’m so envious of Miss Kanae~”

Suma: “Lord Tengen, I want a birthday too~”

“Um… Kanae, everyone’s still watching…”

Hearing Zero’s reminder, Shinobu Kanae snapped back to reality and quickly released the embrace.

She fastened the bracelet around her wrist. Under the light, and with her beautiful face, she looked utterly elegant.

…

After the birthday party ended, everyone returned to their own residences.

Shinobu Michiru had watched everything—something unspoken stirred within him, as if he had lost something.

A thought suddenly formed in his mind…