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Language:
English
Series:
Part 2 of The Heart of a Butterfly Brother (KnY x Twst)
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Published:
2025-11-18
Updated:
2026-03-09
Words:
2,566
Chapters:
31/?
Comments:
174
Kudos:
182
Bookmarks:
12
Hits:
5,768

Heart of a Butterfly Brother Art Book

Summary:

A piece of art of my au

Update: It is now a full ass art book. Somehow.

Chapter 1

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I used a base for this art, it's why the katana looks so bad djifnhbnfb

The blade's both red and pink because of his ability to use both Flame Breathing and Flower Breathing. Like Tanjiro, he hasn't mastered either, which is why he can easily use both.

His haori and leg warmers were a gift from Rengoku, the flowers at the edges of his sleeves were added with Aoi's help post-Swordsmith Village Arc, since he went to help Mitsuri and his haori got damaged.

The butterfly hairpin is inspired by the NRC Heartslabyul uniform.

The handguard/tsuba (the round thing on the sword) is supposed to be shaped like a heart but I could not draw it without it looking weird.

Chapter 2

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He's enjoying his meal!

He has copied his mentors/big siblings' mannerism, it seems! Deuce is confused on what 'umai' means tho.

Chapter 3

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Ace and his dynamics with his siblings!

It's ironic that at first, he felt embarrassed of the attention that would be put on them whenever he and Rengoku used to eat in public (such as like in the Mugen Train mission), and now he does it sometimes.

Chapter 4

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We got 3000 hits already! It's amazing!

I'm so happy you all are enjoying this silly little series! I'm happy making it!

Chapter 5

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A gift from Sebek ;>

For context, I have an rp blog of this Ace au on tumblr, and one interaction was a Sebek rp blog gifting Ace a red ribbon. While Ace would definitely have a hard time taking off his butterly hairpin for anything other than sleep because he doesn’t wanna break the last memory of his butterfly siblings, he would definitely wear the ribbon on special occassions.

Chapter 6

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Scene redraw of the anime's last episode with this au :>

He's fine guys! I promise! Just needed a little cry.

Chapter 7

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Ace's sword! Full design and everything to commemorate that I gave in to my demons and made two tumblr blogs related to this au, a normal rp one and a story rp one asnkkjxqxw

Yes I am fine <— lying

The sheath changed once he began learning Flower Breathing. It actually used to be a plain white without any pattern, similar to Rengoku's.

I'll do the same with Sebek and Leona's swords.

Chapter 8

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Omneshroom asked for a closer look at Ace's hairpin, so here you go!

(You can request specific things you want me to draw about the AU as long as it's been said in canon or we have gotten there, aka, asking me to draw Sebek's demon slayer uniform is alright because it's been revealed he was in the same situation as Ace and Leona, but drawing Ace's reaction to, let's say, the overblot of book 7 is a no go because we have not gotten up to that point yet. This is just with art requests though, I'm willing to give sneak peeks to certain things I have drawn without giving too much context/spoilering the event. Yes, you can ask for SebAce art btw.)

(Also please excuse my ass handwriting lolol)

It's based off the card soldiers and the usual deck of cards. Because Shinobu became such an important figure to Ace, he ended up telling her that he was also from another world. Though she knew that Leona was from Twisted Wonderland because it's information Leona is willing to give to the Hashiras (the first one he told was the master) as he is sometimes mistaken for a demon with animal features and, therefore, has an animal-related BDA, she was surprised that Ace was also from Twisted Wonderland.

He was given the hairclip a little bit after he was taken under Shinobu's wing, after Rengoku's death.

It's also the last memory of her and the other butterfly siblings (except Aoi, since she is now here)

Chapter 9

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HERE SHE IS

I teased a bit on my personal art blog on Tumblr, but I've actually been doing a sprite for Aoi! Though I did trace over Kalim's because his jacket thing is the closest thing to Aoi's.

The earrings are a gift from Ace by the way. He would sometimes bring gifts from his missions for the butterfly girls, as well as for Shinobu.

This did take me several days due to motivation and also school stuff and writing. But now that it's done, I'm so happy.

Chapter 10

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LunarEclipsa1026 asked for SebAce, so I have delivered!

This is set when they're back in Twisted Wonderland, a date gone wrong because of the rain, unfortunately.

Ace is annoyed by the rain because he really wanted to go to the park and have a peaceful time with Sebek and catch up after returning to their world once Tanjiro was turned to normal. Sebek is flustered by the sudden proximity between the two and having to use his jacket to cover them both from the rain.

Chapter 11

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The first out of Leona's two tsugukos! Yes they both took his last name shush.

This is Sunako! She's 17 and the younger twin. She's very much younger sibling core, a little bit spoiled when it comes to her brother but not to the point of it being super toxic or unhealthy. She's also an openly loving person, Ace and Sebek have gotten crushed when being hugged by her and smothered by platonic affection.

Despite her colour palette, she uses Wind Breathing, as she is very much battle hungry when it comes to demons.

Instead of a katana, she uses a naginata! Both she and her twin don't use katanas, they use other weapons.

Chapter 12

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And here we have the older twin!

This is Nagisa, the complete opposite of his sister when it comes to his extroverted self. While Sunako is very bubbly and kind, Nagisa is much more straight-forward and blunt. He takes no bs from anyone. Though he has soft spots for those who are close to him, hence to why he spoils his twin a little bit. He is deaf in one ear.

Like Genya, he doesn’t have a Breathing Style, so instead he uses a bunch of long-ranged weapons and a short sword so he can cut off heads. His favourite is the yumi (japanese bow).

Also I just noticed that his uniform looks like the actual gay flag and uh. That was unintentional.

Chapter 13

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Did somebody order a clobbering?!

*Gets assaulted by tomatoes.*

Okay, yeah, deserved lolol.

ANYWAY I finally finished Sebek's design in the au! I love him with his hair down, my son looking so HANDSOME FOR REAAALLLLL so I HAD to use that for here. Besides, since he's a demon slayer, he constantly had to go on missions, so he barely had any time to slick up his hair. Plus, Ace commented once how he looked better with his hair down, so he decided not to slick it up anymore.

I think the haori sorta gives away a little bit about who he was with, hehehe. I did base it off of Diasomnia's dorm uniform colour scheme. I might change it though, so yeah.

I did not have a better background EKCNKEFEKJEFKN I cleaned my pinterest folder and deleted most of the images there, which was where the backgrounds were... And I forgor...

Anyway, I think that next chapter of the fic should be up next week as long as I don’t drown myself with my other fics lolol.

Chapter 14

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Average gym class with Vargas. Ace thinks it's child's play.

I believe that Aoi, as a previous demon slayer before becoming a nurse and helping with rehabilitation training, has enough stamina to last for almost all of the class. The only reason she can't last all of it, like Ace, is because of her quitting to be a demon slayer.

Chapter 15

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Leona and Sunako when she was trying to bribe him to take her and Nagisa as his students. They became his tsugukos a year before canon.

He is very obviously teasing her out of sheer amusement, but he is genuinely impressed by how stubborn Sunako is about him taking the twins under his wing.

Chapter 16

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"Bon, bon, bon, bon, bon, bon, bon, bon

Searching for my friends, bubbling away

Bon, bon, bon, bon, bon, bon, bon, bon

I don't want to be alone, I'll leave this place today."

—Bon Bon Jellyfish Planet (VIVINOS + C!nah)

 

Look at my babies. I love them. I sure hope nothing terrible happens to them.

Chapter 17

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A more-so what if.

What if Ace had turned into a demon, and still chose to fight by the side of humanity? Things would have surely gone different, both in the kny canon and in the twst canon. And S.T.Y.X would have most likely noticed about the sudden return of the missing people, and yet this one boy has severely changed.

He works for S.T.Y.X, who also monitor him after they investigated him and found out about his new genetics and new... diet. He is a bodyguard for Idia and is also allowed to clear out the Phantoms whenever the alarm at S.T.Y.X goes off. He and Ortho enrolled at the same time, so they're both first-years. Again, he is put in the middle child position, as Idia is older and Ortho is younger. Physically, at least.

He is the one who reports to Idia about the overblots.

Chapter 18

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"Your herbivores are overcomplicating this. If we judge the kid here, without Oyakata-sama present, we'd be going against his orders. Honestly, the fact that you believe this is within your rights means you believe your judgement is above his."

Sand Hashira: Kingscholar Leona

'That man... he has ears on the top of his head! Is he a demon? But how can he stand out in broad daylight?!'

"They should be given, at the very least, a chance to plead their case and explain themselves. This is supposed to be a trial, after all. If we denied them that simple right, we would be abusing our higher status as Hashira."

"Leona-kun is right!"

"What, you defendin' kids now, Kingscholar?"

"No, Shinazugawa. I'm simply stating facts. Frankly, the idea of a hervibore parading around with a carnivore while working for the corps is straight up nonsense. But the runt's gonna lose his head sooner or later, just like every other slayer. So why not entertain his delusions?"

'Guh! He's looking straight at me! His gaze is so intense! Almost like a predator observing his next meal!'

"So, if anyone does somethin' to the box while Oyakata-sama ain't here? I'll be the first one to retaliate."

 

Leona sometimes refers to demons as carnivores as an insult. Nezuko, Yushiro and Tamayo are the ones that are exempt to this treatment.

Chapter 19

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"What's up, Sebek-chan? Why so red?"

"Hmph."

 

What if we were girls in NRC? And we had romantic tension and unresolved feelings?

Female Ace would so imitate Kanao's hair style but also leave it like half up half down.

ALSO HEAR ME OUT ON BUTCH SEBEK. LIKE. DO YOU SEE THE VISION??? SHE WOULD BE SUCH A BUTCH, BUT ALSO ENJOY A BIT OF HER FEMININE SIDE WHEN SHE'S WITH ACE.

Chapter 20

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"I always thought that being desperate was for losers. I've always been able to handle things without putting much effort into them. And if I couldn't... I ran."

"And yet, seeing him work so hard, while I stood in his shadow. I must have looked pathetic, huh. I could never live up to the Rengoku name. I could never fully master Flame Breathing. How can I be his successor? How can I be his student?"

"If only I was like him. Appearing and leaving everyone in awe because of his strength and resilience... And I can't do that... I can't be as strong as him."

Chapter 21

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Happy Valentine's Day, everyone!

Sadly I don't have enough time to finish them because fuck History of Art, so I leave you with these unfinished chibis of the five!

Chapter 22

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"What’s wrong? Why do you guys look like you've seen a ghost?"

'THERE’S NO WAY THAT’S ACE!!'

 

What-if scenario! What if Butterfly Brother Ace got swapped with canon Ace! How would everyone react?

Right off the bat, the first years would be so fucking freaked out. Because, what do you mean this is Ace? There's no way. He's not making any snarky remarks or being a little shit (/affectionately). To them, this is just someone who looks like Ace, but does not act like him.

Meanwhile, Butterfly Brother Ace is very confused. The first years are just eyeing him like he's an alien, or something like that. It sorta makes him uneasy, but he knows he doesn’t have to raise his sword at them because they're not man-eating demons.

 

I'll get better at drawing Jack and Epel, I promise-

Chapter 23

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I finally got around to drawing Yuu! They're very friend-shaped.

And yes! They are a descendsnt of Giyuu. They’re Giichi's (the kid from the end of the manga) younger sibling!

Chapter 24

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Meme redraw!

Jack does not want to attend the basketball club's games with Sebek for this reason specifically.

However, Jack also likes to hang around Sebek because he's pretty cool. And he also finds Ace cool. I mean, he's been following Ace pretty much since he started his Magicam account.

Chapter 25

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I tried.

I really tried fsinfdnkfdkjfdjk

Chapter 26

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Ace sketch of him and some butterflies! He likes them very much!

The butterflies like him, too.

Chapter 27

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An unexpected crossover has appeared in the wild!

So there's a fic here called Crossroad's Gift which updated today and it's a PJO x TWST crossover and the author is also on tumblr so I drew fanart of their Yuu and Butterfly Brother Ace meeting. You guys should totally read it because it’s really good.

Even if I'm not in the PJO fandom.

(Also the creator themselves confirmed that Ace would need to be sitting down or crouching to reach this Yuu's height. Which is very, very funny lol)

 

In case you can't read the text:

Yuu: "Where did you even get this?"

Ace: "It was forged for me."

Chapter 28

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Local big brother figure reverts back to his asshole self for a few seconds, comes to regret it instantly later.

Him afterwards:

On a side note, I like the Ironmouse song

Chapter 29

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More sketches on Demon Butterfly Brother Ace (ignore how one of the sketches has Ace missing a leg, my dumbass forgot to draw it)

I actually really like Styx's uniform, I think it's one of my favourite organization uniforms I have seen so far. My favourites are the Team Aqua and the Aether Foundation uniforms from the Pokemon series

He wears a hoodie with his uniform like Jamil, he just wears it up to hide his appearance and try not to draw attention to himself. Most would think he's an Ignihyde student that just so happens to go out more than the rest. Nobody expects him to be from Heartslabyul.

Some are also curious about the 'tattoo' on his face. Others are curious about his 'magic' (his BDA). Overall, he's a mystery to most.

 

I can't believe I made so much lore for this divergence of an au... This is Caprice all over again.

Chapter 30

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More fem SebAce.

They're so silly, chat.

Chapter 31

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The lion does not concern himself with anything other than his naps.

And his cubs. Especially his cubs.

Also yes, he named the crow Falena. He misses his family, regardless of his resentment to them.

 

Ignore the Trey doodle under the paper, it's for another au of mine.

Series this work belongs to: