Zenitsu considered himself both lucky and unlucky, three days ago he had been sent on a mission because apparently he wasn't injured enough to get some rest, and he was all alone too!

The lucky part comes in because by chance, another Demon Slayer had taken care of the Demon Zenitsu was sent after so he never actually had to fight it, at first he had to search the streets of that little town at night to find any Demon activity, he found the Demon sure but approaching it would just be a deathwish on his side, so he remained on a distant, shaking and hoping the Demon wouldn't find him instead.

And a few minutes later, another Demon Slayer showed up and killed the Demon in question, meaning Zenitsu's mission was technically complete aswell and he could return to the Butterfly Estate, which was exactly what he was doing right now.

During the walk, or run, back to the Estate Zenitsu found himself wondering about the Kamados, last time he saw Tanjiro was at Mount Natagumo and back then his face looked eerily much like the rest of the Demons he had encountered on that cursed mountain and he never got an update on their situation, so from what he knows they might've very well killed Tanjiro, Zenitsu half-panicked when he considered the possibility that he'd never hear the boy's calming sound again.
Zenitsu never expressed it, but Demons normally have such a nasty sound themselves that radiated their intent to feed, and to kill him.
Tanjiro carried that sound too, he was a Demon afterall, but he also carried such a calming and kind sound that made Zenitsu feel kind of fluffy whenever he'd actively listen to it, which is what he actively did back when he was resting with them in the Wisteria House.
"If- If they killed him… If they killed him, I'll give them a piece of my mind!" Zenitsu angrily cried to himself during this mental 'revelation'.

His mind almost drifted off when he nearest the Butterfly Estate, he began hearing a girl's voice, a very familiar one that sounded almost tired, it was Nezuko-chan.
Zenitsu figured she was likely training again, they all had to do that the first time they got to the Butterfly Estate, and then another sound shot through his ears as he reached the gate.

Someone coughing, it was a boy, he could tell that much.
No, not just a boy…
It was Tanjiro.

"Onii-chan, you don't need to push yourself so hard." Nezuko said while her breathing was ragged due to exhaustion, by now she had been trying to teach Tanjiro Total Concentration Breathing - Constant for hours and the boy refused to take a break, just now he had choked on his own breath as he tried the technique again.

After the coughing fit the two siblings exchanged looks and erupted into a laughing fit, they both knew Tanjiro was sometimes a workaholic and getting to learn a new skill so powerful was something he'd rather learn fast so he can go back to Demon Slaying with his sister.
"You know, Onii-chan. Even without Total Concentration Breathing - Constant you're already really strong." Nezuko said as she looked back on their test matches from earlier, the same matches that helped Nezuko tire herself out so much.

Suddenly however, the doors to the training room flew open and the Kamados perked their heads to face the opening, right there stood the blond-haired Slayer they'd know so well by now with tears almost flowing from his eyes, "Tanjiirooooo!" Zenitsu said as he flung himself at the boy in question.

"Zenitsu!?" The two Kamados yelled out in unison from the boy's sudden action which knocked Tanjiro to the ground, "Hey, calm down, what's gotten into you!?" Tanjiro continued after, earning a confused look from the boy who raised his head to make eye contact before the Demon boy shoved him off, Zenitsu grunted as he fell onto the ground and Tanjiro stood up again, looking rather concerned.

"H-Hey… Tanjiro, you can talk now?" Zenitsu said in a low tone, earning a sigh from Tanjiro in return who just smiled after, giving Zenitsu a bright and cheerful "Yep!" to solidify the deal.

"It's kind of a shame, we worked so hard on a language for you because you couldn't talk. I guess we don't need it anymore, huh?" Nezuko asked, she had a point, Tanjiro barely got to use the language they made because of the extreme turn of events that had chased the Kamados around like bad luck, and now Tanjiro had regained his ability to talk seemingly out of the blue, well Nezuko knew better, she had been told what Marechi is for Demons and she already figured that the incident during the trial resulted in Tanjiro getting a lot stronger overall, and apparently even giving him his voice back.
"We can still use it, for when we need to be quiet." Tanjiro answered with a cheerful tone, "We can't always shout to each other when fighting a Demon so having a sign language could prove useful." Tanjiro elaborated, to which Nezuko nodded firmly.

A short silence ensued, and Zenitsu decided to break said silence with a question of his own, "Say, what are you two doing actually?"

"I'm trying to teach Onii-chan Total Concentration Breathing - Constant, but he's so stubborn that he refuses to take a break." Nezuko answered with her hands on her hips, but it was clear Nezuko actually kind of endeared her brother's behavior, it just showed her that Tanjiro's personality hadn't changed, even now.

Tanjiro laughed suddenly, "I think we could take a break now, since Zenitsu finally came back." he said after, getting a relieved sigh from Nezuko in return who also briefly laughed after.

A few minutes later, everyone had seated themselves on the floor still inside the training room, Tanjiro and Nezuko decided to catch Zenitsu up-to-date with their experiences including the Trial, hearing about that part made Zenitsu hot with anger but he continued to listen.
Poor Tanjiro had to endure effective torture just because one of the Hashira decided that he particularly didn't like Tanjiro, it was made worse by the shift in sound Tanjiro emitted while that part was being explained, it shifted from such a happy and kind sound to a rather somber one with a tinge of fear.

"...I was so afraid I'd lose myself." Tanjiro had said during the explanation and at that moment Zenitsu decided he had enough, suddenly perking his head upwards the blond-hair boy grabbed it and relentlessly unleashed his own anger.
Tanjiro and Nezuko were used to this kind of behavior, but only when Zenitsu was particularly sad or scared, seeing him do it while angry instead silenced the siblings as they stared in disbelief.

"YAAAAGH! HOW COULD THEY!? HOW COULD THEY!? I'M GOING TO MAKE THEM PAY, DAMMIT! I DON'T CARE IF I GET HURT, WHY WOULD ANYONE WANT TO DO SOMETHING TO HORRIBLE TO SOMEONE SO NICE!? I DON'T UNDERSTAND WHAT KIND OF LOGIC WENT THROUGH THEIR HEAD! AAAGGHH!"

Zenitsu's yelling caught the attention of some of the staff which was apparent when Aoi suddenly came into the training hall with a half panicked and half annoyed facial expression, Tanjiro waved as he noticed the girl enter while Nezuko remained silent, not knowing how to react at all in the moment, "What's going on here this time." Aoi simply asked as she looked at the trio sitting in the room.

"Zenitsu is a little angry." Tanjiro said while keeping his smile and glancing at the blond boy who had by now stopped shouting and was staring at Aoi aswell, "A little?" Aoi responded while giving Zenitsu nearly a death glare, "I think it's more than a 'little'. He's never been this loud because he was angry before." she said with a sigh.

Tanjiro shrugged in response and looked over to Nezuko to see if she maybe had something to say, but the girl just looked at Tanjiro with a worried expression evident on her face.

"Sorry…" Zenitsu managed to stammer as he got into an upright sitting position instead of being almost folded backwards onto the ground, "It's just… It's so mean! Why'd they have to treat Tanjiro like that!?", without skipping a beat Aoi immediately responded to the boy's question by simply stating "He's a Demon, and his nature hasn't been seen ever before. They had all the right reasons to be skeptical."

Now there was an awkward silence, everyone kept exchanging glances before Nezuko rose her hand and finally spoke, "I think we should change the topic.", everyone nodded in agreement.

"Zenitsu, would you like to help me teach Onii-chan?" Nezuko said as she mustered a smile, getting barely any response from the boy she asked, Zenitsu had his reasons not to respond to a question like this which mainly involved not wanting to get back into action right after returning from a mission, or generally trying to stay out of harm's way.
Except there was one component that really made Zenitsu consider it, Nezuko herself.
Apparently, his face had started to drift off to his lovey-dovey expression again because Tanjiro butted in with a "I think Zenitsu has something better to do." in a slightly aggressive tone, it immediately brought Zenitsu back to his senses and he profusely apologized before running off in order to try and not make the situation any worse.

"So he's still trying to flirt with you?" Aoi asked as she looked at the fleeing blonde, Nezuko just gave Aoi an awkward laugh, "Hey, Aoi." Tanjiro suddenly said to get the girl's attention who turned to face him with a curious expression, "It just so happens that some of my important items are still on the mountain, do you think you could get someone to collect them for me? I-It's okay if you can't or if it's not important enough but-!"

"Alright, I'll ask Kocho about it later." Aoi suddenly said, cutting the boy off entirely as he had already started to rant on.

"Thank you!" Tanjiro blurted out louder than necessary, getting a laugh from his sister in response.

Weeks passed and the Kamados had built an effective routine for them to get as much out of their time as possible, which included a good night's rest, breakfast right after, separate morning routines and then lastly Tanjiro learning Total Concentration Breathing - Constant, since two days ago Tanjiro had already started blowing into Gourds to test his progress and he was clearly catching up to his sister quickly.
After all this, they gave themselves the rest of the day free.
Luckily, Shinobu had accepted Tanjiro's requests for his items to be fetched and for the letter he had sent to be delivered.

Tanjiro had also been able to reconcile with Inosuke and the two had started to somewhat bond, well, as much as Inosuke was willing to show at least.
Knowing Inosuke he'd constantly challenge Tanjiro to duels and playfighting, each time Tanjiro wanted to decline so badly but he couldn't find the resolve when he'd catch a whiff of Inosuke's giddiness.
Eventually, sparring with Inosuke became routine for Tanjiro aswell and it helped the two boys become stronger greatly.

As of yet, Rengoku's response hadn't arrived although the Kamados were sure they'd return to the estate after they'd encounter their next powerful opponent which gave them plenty of time to get a response.

Eventually, everyone had recovered and Shinobu was doing one last checkup on Nezuko, "You've fully recovered." Shinobu said with her usual smile, "Sorry I can't see you off, but good luck in the future okay?"

"All right! Thank you!" Nezuko responded with a cheer of her own while she left Shinobu's office, humming to herself while she walked through the Estate.

"Alright, time to go!" Nezuko said to herself before her ears caught the footsteps approaching from a corner, "Ah, someone's coming.", she thought as she moved herself to the side of the hallway as to give the person room, except that person had different plans and instead still bumped into Nezuko before they continued to walk to wherever they were headed, Nezuko let out a soft groan as the rather large built boy bumped into her shoulder.
"Must not be in a good mood…" Nezuko thought as she looked back, suddenly recognizing the very specific hairstyle the person in question had, without missing a beat she suddenly shouted after the boy "Hey! Long time no see. How have you been!?", except she didn't get a response as the boy merely kept walking, Nezuko sighed and figured she'd go say goodbye to Aoi.

"Oh, really? You're already leaving? It wasn't long but I'm glad we got to spend some time together." Aoi said after Nezuko caught her up-to-date, "Thank you." Nezuko said with a small laugh, "Take care." Aoi responded in return while still tending to the blankets she was currently hanging outside.

"Thanks for all your help." Nezuko continued, "Thanks for taking care of us all, because of you we're able to fight again.", The girl gave Aoi a wide laugh right after, Aoi was silent for a bit as she processed it, but then sighed, "I'm not as important as you guys, so you won't have to thank me."

"That doesn't matter. You helped me, Aoi. I'll think about you when I go into battle. If I get hurt again I'll ask for your help!", mid sentence Nezuko had already begun running off, waving happily to Aoi who was left to silently process what Nezuko had said.

In the meantime, Tanjiro was packing things and saying goodbyes aswell, until he found someone, a girl that Tanjiro had been curious about for a while.
He had met the girl a few times throughout his stay here and he even partook in some of the challenges Aoi usually prepared for injured Demon Slayers, not many came and went but it was still active enough he'd sometimes be able to play one or two games.

The girl was sitting on a patio of the Estate, staring outwards towards the sky, Tanjiro decided to give her their goodbyes now before he'd run out of time.
"Kanao!" He called out, causing the girl in question to turn her head around to see the Demon Boy standing a few meters away from the door opening as to avoid stepping too far out, "We're heading out, thanks for everything."

Kanao gave Tanjiro a silent and soft grin.

"You're pretty amazing, we've been in the corps for almost the same amount of time and you're already Shinobu's Tsuguko, we'll work hard too!"

Kanao kept giving Tanjiro a silent and soft grin, an "Uhm." escaping from her mouth.

The two stared at each other for a bit in silence until Kanao took out something from a pocket, a small coin.
She tossed it and caught it on the back of one of her hands while using the other to secure the coin, as she lifted the covering hand to reveal the coin had landed on Tails she turned to face Tanjiro again and responded to him, "I merely followed by teacher's instructions, so you don't need to thank me. Goodbye."

"She spoke!" Tanjiro though in silent disbelief, from his experience Kanao was a shy and quiet girl who barely did anything generally, he had tried to talk to her a few times before but barely ever got an answer, "What was that you just threw into the air?" he asked excitedly.

"Goodbye."

"What is that!?"

"Goodbye."

"Money? It said 'front' and 'back', Head and Tails? Why did you do that?" Tanjiro continued asking, he had gotten a little closer and was now sitting on the floor near Kanao who continued to remain silent, "It really spins!" Tanjiro continued.

Eventually Kanao gave in, revealing the coin she had tossed into the air moments before in the palm of her hand while she turned to face the boy asking her questions, "I use this to decide things for which I haven't been told what to do. Just now I decided whether I would speak to you or not, Heads meant I wouldn't and Tails meant I would, it landed on Tails so I spoke to you. Goodbye."

"Why can't you decide for yourself?" Tanjiro continued, still curious about the girl and now that he made her talk, twice, he wasn't going to give up, when Kanao remained silent Tanjiro continued, "What did you want to do yourself?"

"It doesn't matter. Nothing matters at all so I can't decide by myself."

"I think everything in this world matters. I bet… Yeah, the voice in your heart is soft, but it's also important to follow instructions… Can I borrow that?" Tanjiro said as he pointed at the coin, to which Kanao only managed to stammer a few confused sounds before a soft unsure "Yes…" came from her, "Thank you!" Tanjiro said as he quickly took the coin, stood up, and backed up a bit into the Estate where the roof was a bit higher, "All right, I'll flip it to decide!" He said excitedly as he readied himself to toss the coin, "Decide what?" Kanao asked in confusion as she watched the boy do his thing.

"Whether or not from now on, you'll listen closely to the voice in your heart! If it comes up Heads you'll have to live by your heart!", with that Tanjiro tossed the coin up high causing it to quickly hit the ceiling and fall back down, Tanjiro shuffled around quickly to position himself ready to catch the coin and he soon did, "I got it! I got it!" he yelled as he readied himself to show the result, Kanao herself was getting anxious and impatient, she wasn't able to see the coin land due to it's sudden speed coming back down and the speed at which Tanjiro caught it, "Which is it?" she repeated to herself as Tanjiro lifted his hand to show the result, it had come up Heads and Tanjiro immediately rejoiced, "Kanao!" he said with vigor as he gave the girl her coin back, "You can do it, the heart is what drives us! Your heart can grow infinitely strong!", he finished and let go of Kanao, running back into the Estate to continue his own series of goodbyes, "W-Wait!" Kanao managed to cry out before the boy had left, "How did that come up heads!?" she demanded.

"It was just chance, if I had gotten Tails I would've just tossed the coin over and over until I got the result I wanted. Take care!" with that Tanjiro had left, leaving Kanao to digest the new information.

When everyone had gathered outside to give the fully dressed Demon Slayers their goodbyes the situation was bittersweet, everyone had grown to like the strange group of Slayers that had made the Estate their home for a while and saying goodbye was going to prove difficult, but they powered through it and before long they were back on the road, of course Tanjiro had his protective items back on to shield himself, just like that the group sat out.

Welp, Butterfly Estate will probably see these guys again in the near future. There's a bunch of new Demons on the loose ready to take Tanjiro into custody afterall.