Upon defeating Upper Moon Four and being able to withstand sunlight, Nezuko found herself faced with a new obstacle: relearning speech. It wasn't overly difficult to acquire words, but arranging them into a coherent statement was much more daunting. So she thought it'd be best to start small and to first expand her vocabulary. With this task in mind, she sat in the Butterfly Estate, listening attentively to Kanao, who was changing the bandages on a comatose Tanjirou. As Kanao carefully wiped around a wound, she remarked, "This medicine stinks."

Nezuko echoed, "Stinks?"

"Yeah. The stuff I'm cleaning him with." She extended the bottle to Nezuko, who sniffed and then declared, "Stinks!"

"That's right. Here, Tanjirou, you smell it." Kanao held it near him, and he frowned as his nose made small puffs of displeasure. They laughed, and when Nezuko doubled over, leaning on the bed, Kanao cautioned, "Careful! He broke his leg badly."

Nezuko sat up, gasping, "Broke!" and she smoothed his sheets apologetically.

"It's alright. You know what'll make things better?" Kanao moved the bottle near his nose again, and Tanjirou scowled and muttered in his sleep, "I hope you get busted for lying, coward…"

Nezuko guffawed, "Busted!" and Kanao laughed, "Is he talking about the Upper Moon? The odor must be giving him nightmares, but this bottle's almost empty. Could you grab another one from the medicine cabinet?"

Nezuko set off on this quest, but a racket from the kitchen caught her attention. Curious, she opened the door, slipped in, and found Genya and Inosuke peering searchingly underneath and behind the cabinets and appliances. Without looking up, Genya snapped, "Why'd you open the door? It'll escape." Inosuke retorted, "It wasn't me. It was her."

Genya straightened, spotted her, and said sheepishly, "Oh. Nezuko. Sorry, I thought Inosuke opened the door." She gestured at them and asked, "What...?"

"You're wondering what we're doing? We were supposed to be cleaning, but now we're trying to catch a mouse. We'd be done already if it weren't for somebody being dumb as shi—" Genya halted, gulped, and corrected, "Brainless. If it weren't for somebody being brainless."

Nezuko questioned, "Brainless?" but before she could get an answer, Inosuke shouted at Genya, "Take that back, motherfu—"

Genya interrupted, "Tanjirou will end us if she learns to curse," so Inosuke resorted to grumbling, "I'd rather be brainless than Breathless."

Rage flashed over Genya's face as he prepared to counter, but then he suddenly exclaimed, "There it goes!" as the mouse sprinted by. The boys scrambled after it, but their pursuit was unfortunately fruitless. Already on the brink of conflict, Inosuke couldn't contain his frustration, and he yelled accusingly at Genya, "You dum-dum! I would've gotten it if you weren't in my way!"

"You were in my way! It was right in front of me! Why'd you push me aside?!"

"That wasn't a push! This is!" Inosuke shoved Genya, who retaliated with an even fiercer shove, and soon they'd devolved into a brawl and forgotten entirely about the mouse. Nezuko watched with alarm, decided it'd be unwise to stay, and continued onwards to the medicine cabinet, which was in a storage room that required passing through Shinobu's office. The office was presently being tidied by Aoi and Zenitsu, who'd been assigned this chore to prevent him from being noisy over Nezuko. He brightened upon seeing her, but he didn't dare make a sound because his captor gave him a warning glare.

Aoi's attention was diverted though when there came a distant thud from the kitchen followed by Inosuke roaring triumphantly, "Get shitted on!" Only a few seconds later, there came another faraway sound: a crash along with Genya snarling, "Who's shitting on who, huh?!"

Aoi grumbled, "Those two had better not be fighting in there," as she took a broom for a weapon and headed to the chaos.

The instant she was gone, Zenitsu clutched Nezuko's hand and whined, "Nezuko-chan, I've been wanting to talk with you, but Aoi's being mean." She soothingly smoothed her thumb over a bruise on his knuckles, and he said, "You're too sweet for worrying about me! It's nothing, just a bump from the mission I had while you were in the Swordsmith Village. I was thinking about you the whole time, and right after finishing my work, I went and got you something."

He handed her a palm-sized box, and she opened it to reveal a compact mirror. She traced a finger over its cloisonne shell and made an awed noise, and he gushed, "Now you can see how lovely you are all the time!" As a poor country girl unused to handling fine things, she said hesitantly, "Money…"

"You're worried about the price? Don't be! I can take care of you! I'm not a bum!"

"Bum?"

"That's what those two idiots in the kitchen are. Anyway the place I was at, it's really busy, so there were tons of neat things to see. There was—" but Aoi's voice interjected, angry and scolding: "God help you both if I come back and the kitchen isn't spotless!"

As her footsteps approached, Zenitsu whispered hurriedly, "Ack! She sounds mad from confronting those two. We'll talk more tonight? The fireflies are starting to appear, and we could watch them while we chat."

"Tonight!"

"Yes, tonight! You'll be with Tanjirou, right? I'll come get you."

She nodded, collected the medicine, and then passed by Aoi, who resumed her position as Zenitsu's jailor. Upon the delivery Kanao said, "Did you get distracted? It's okay. There was just enough left in this bottle. We'll save that one for tomorrow." She set it on the nightstand, said her goodnights, and then left the Kamados. Because Tanjirou was in a fragile state, he'd been given a private room to optimize his rest, so with nobody and nothing to occupy Nezuko, she kept the door open, watching the number of passersby declining as the Butterfly Estate sank into sleep. She, however, remained awake because she was expecting Zenitsu, but unbeknownst to her, he'd accidentally fallen asleep. How fortunate for his mistake because her wakefulness allowed her to see something suspicious: a boy passed by the door once and then again, glancing warily up and down the hallway the second time before entering the room and making a beeline for Tanjirou's belongings.

The Estate offered lockers, but the demon slayers operated well enough on an honor system that the lockers were rarely used. Lately though the honor system was failing because there'd been a string of thieveries, and this fellow seemed like the culprit. Nezuko wouldn't hurt humans, but she jumped up, extended her arms protectively, and struggled to say something to shoo him. He was briefly frightened, but when she could only blurt, "Hello?!" he scoffed, assumed she was dumb and harmless, and walked around her to pull Tanjirou's suitcase from beneath the bed.

Screaming seemed inappropriate, so she strained her mind to try and utilize what she'd learned that day. The first word that surfaced was a lesson from Kanao: "Broke!" The thief stared at her, unsure of whether to laugh or to be insulted, so he settled on shaking his head and resuming his business. She rushed to produce another word, and since alliterations are memorable, her second utterance was a copying of her unconscious brother: "Busted!"

"Shut up!"

But she wouldn't shut up because speaking had given her the momentum to more easily recall her friends' talking, so she continued the attack, courtesy of Genya: "Brainless!"

"I said shut up!"

"Broke, busted, brainless!"

"What's with you?!"

"Bum!"

"Oh for crying out loud..."

"Broke, busted, brainless bum!"

"Get lost!"

The sound of knocking startled them, and they turned to find Genya, Zenitsu, and Inosuke standing in the doorway. Her shouting had roused them, and Genya and Inosuke pounced on and restrained the villain. Inosuke commanded, "Nyanko, punish him! Bite his hands off!" She made a bewildered noise, and Zenitsu cried, "No! Let's bring him to Shinobu!"

Inosuke ignored Zenitsu and urged, "Do it for your brother!" She hesitated but then shook her head, knowing that Tanjirou wouldn't approve, so Inosuke warned, "Kenma will do it if you don't."

Genya was much more willing to maim than her, and he wrestled their prisoner's wrist into a suitable position for biting until Zenitsu shrieked, "No!" which spurred Nezuko to tug Genya backwards and away. The sight of Genya's sharp teeth and the threat of amputation was beyond terrifying for their captive, who broke free from Inosuke and leapt through a window. Although Nezuko was relieved that he wasn't mutilated, she was still sore that he'd aimed to rob Tanjirou, so in imitation of Inosuke, she yelled after the retreating would-be thief, "Get shitted on!"

"Nezuko... what're you saying...?" The groggy voice belonged to Tanjirou, who'd finally awoken because of the pandemonium and who appeared horrified that this was how he was welcomed back to consciousness. Despite her soiled mouth, Nezuko gave him the brightest of smiles.