Author's Note: Hiii its me again! I'm back after a while with a new story! This one's based Demon Slayer Kimetsu No Yaiba. I recently got into the series and I fell in love with it. But I noticed there were NO sickfics of it on here. So to my disappointment I thought, okay time to take matters into my own hands here! And after a few months of thinking, I got this interesting idea. And I'm aware that the manga confirms that demons can't get sick, but hey Nezuko's a unique demon so maybe she's an exception) It'll be a bit more intense than my usual fluffy fics, this one has a bit of a story arc to it. As usual I hope you enjoy and I hope I do these characters justice or get their personalities right in the writing because I've only been into this series for a couple months.

This may also be my longest fic yet. I have some plans for this one c:

Chapter 15: Nezuko's in danger biting Tamayo due to her enchanted blood! How can they calm her down? Tanjiro can think of one thing. But he'll need the doctor's help this time!

Tanjiro and Yushiro were both shocked at the scene before them as they saw Tamayo's face tense up a bit within being bitten by the ill demon, but she was more surprised than in pain. Cutting her own skin was the norm for her.

Tamayo looked down with gentle yet pitiful eyes towards the small fever-stricken girl below her. She could tell she was just frightened and confused. Nezuko looked up at Tamayo still growling as her fangs sunk into the flesh of the demon doctor's hand, staring her down with her bloodshot eyes looking like she wanted to kill her. But she was too weak to do anything more than this.

One thing however eluded Tanjiro's mind. Well, no. Two things. How could he help out, and would Tamayo's enchanted blood intoxicate Nezuko while she bit her?

Tanjiro's thoughts were cut off quickly by Yushiro's enraged growl upon seeing his beloved Tamayo injured by this ungrateful brat.

"You…. you hurt Lady Tamayo…" he silently said under his breath, a great wave of dark malice filling the room around him. "You…ungrateful…little BRAT! I'LL KILL YOU!"

Tanjiro immediately grabbed Yushiro trying to hold him back. "I'm sorry for what she did!" Tanjiro apologized regretfully on his sister behalf.

"YOUR APOLOGIES MEAN NOTHING!" Yushiro was truly blinded by rage, using his claws to try to attack Tanjiro to get him off. But soon there was another demonic malice that Tanjiro could feel. It was from Tamayo.

"Yushiro…don't you touch him." Tamayo said in a very low and threatening voice. Intimidating both of the boys causing them to both sit down looking down.

"Forgive me Lady Tamayo…I was just…you got injured." Yushiro replied regrettably under his breath.

"I'm a demon Yushiro. This is nothing. Besides, she's just frightened." The doctor responded before looking down at Nezuko looking the same but with even more bloodthirst in her demonic eyes. "…I was able to give Nezuko an injection a while back and because she wasn't weak or panicked, it did not phase her. But given the condition she's in, she was probably shocked from it, and it caused her to get defensive thinking she was being attacked."

Yushiro just remained quiet after Tamayo finished her hypothesis of her patient's behavior.

"I'm still so sorry about this Miss Tamayo." Tanjiro apologized bowing his head in regret of his sister hurting the hand that was only trying to help her. She truly was acting like a feral animal now in her fever-stricken delirium.

"There is no need for you to apologize Tanjiro." She responded. "However, if she continues to bite down on me too deep, my blood might cause her weakened condition to get worse… It only made her doze off the last time I exposed her to it, but this time…she's too weak and there's no telling what effect my blood will have on her if she exposes herself to it this time."

Tanjiro got up and wanted to try to pry Nezuko off Tamayo, but then he hesitated. He worried she would bite him next. Then if she got a taste of her own brother's HUMAN blood, it would be all over.

"Tanjiro. Do you know of anything that might settle her down or at least cause her to knock her out and have her stop biting me?" Tamayo asked looking up at him still not being phased by Nezuko's fangs in her hand.

Tanjiro thought for a moment. He wanted to turn to the lullaby that he sung to her from their mother that would calm her unconscious state down if her fever ever spiked. But this was a bit more complicated. Nezuko was awake and her mindset was way off. But she was probably more self-aware, and he was not sure if his voice would even reach her.

Plus, Zenitsu was right. He was tone deaf. Probably not the person that could calm down a sick and feral demon with his awful singing voice. Nezuko's eyes looked like they lost all sense of herself. She was embracing her demon side now; he was honestly grateful she was too weak to do any more damage than this.

Think Tanjiro, Think!

He thought hard and then realized maybe his voice wouldn't reach Nezuko. But maybe another voice could. A voice that sounds similar to their mother. A woman's voice…

Wait.

What about Tamayo?

He turned to Yushiro thinking he knew everything about Tamayo. He'd be surprised if he didn't.

"Yushiro." Tanjiro whispered. "Can I ask you a question about Tamayo?"

"What!? What do you have in mind!?" Yushiro snapped back thinking too far ahead again.

"Calm down it's okay! I just want to know… Can Miss Tamayo…sing?" he asked a little sheepishly. He was thinking this was a weird question to ask but he thought it would be the key to calming his feral sibling down.

"Wh-what?!" Yushiro was in shock by this question. He actually never heard her sing before. "W-well…no. She…has never sung before. I'm not sure." But he had a bit of a flushed look on his face. Almost as if he wanted to find out what her voice sounded like in song.

"Hmm… Well, I'm going to make her try." Tanjiro said with determination in his voice.

"Y-yes… Do whatever you want." Yushiro was completely lost in his world. What beautiful singing performance would his perfect and beautiful lady Tamayo have in store for him? He was almost excited to find out.

Tanjiro then stood up and walked beside the demon doctor and his feral sister.

"Miss Tamayo. I think I may know a way to stop Nezuko. But I'll need your help with it." He said as he sat beside her.

"Alright, just tell me what I have to do." Tamayo said looking to Tanjiro waiting for what her instructions were.

Tanjiro looked down to Nezuko then back to Tamayo as he began his explanation.

"There was one thing I did to help Nezuko calm down whenever she had fits in her unconscious state due to a fever spike. Before Muzan killed my family I remember long back my mother always sung this specific lullaby to Nezuko whenever she wanted to hear it. It made her really happy. But the first time she heard it when she wasn't a baby, was a time she fell sick just like this, except she was a small human girl." Tanjiro blushed a little bit feeling a little nervous to ask this question to the female demon before him.

"Miss Tamayo…. can you…can you sing it to her?" Tanjiro tried to get the words out without making a fool of himself, and not angering her biggest fan behind him. Luckily, he was completely distracted by his own imagination. It made Tanjiro cringe a tiny bit.

"You…want me to sing this song to her?" Tamayo asked making sure she was up to speed with what Tanjiro had said.

"Yes. Please try Miss Tamayo." Tajiro said.

Tamayo pondered for a bit. She hadn't sung once ever since she became a demon by Muzan after she lost control and murdered the rest of her family. It caused her to look back on painful memories. But foggy as the memories were, they suddenly came to her. As a human, she remembers she also would sing to her own children as well. She used to be a mother herself. But could she still sing after such a long time?

"Miss Tamayo, are you alright?" Tanjiro asked noticing a small look of sorrow upon her face as she thought this over.

"Oh… I apologize." She responded trying to snap out of it. "May I ask…why you cannot sing it to her?" she asked feeling a little hesitant.

"Well…I think it wouldn't work since she's awake. Before when I did it, she was unconscious. And I have been often told when I sing, I'm tone deaf, so I think Nezuko needs someone with an actual singing voice to help her snap out of it this time."

Tamayo looked down to Nezuko. She was starting to bite down deeper.

"Okay, but I don't know the song… Can you demonstrate?"

Tanjiro nodded before he began singing out the lullaby in his poor tone-deaf voice. Tamayo listened respectfully despite internally cringing at the young demon slayer's awful singing voice. Surely, she couldn't sound this bad…could she?

He sung the whole song but just as he suspected, Nezuko wasn't phased in the slightest.

Tanjiro sighed. "Sorry you had to hear that…" he admitted embarrassedly. "Do you think you can try to repeat after what I said?"

Tamayo nodded. She was intuitive enough to memorize each word and each lyric.

"Alright." Tamayo said. "I think I got it. I will do my best…" she said sounding a little nervous.

Tanjiro said one more thing. He remembered the flashback to him watching his mother take care of a bedridden young flu stricken Nezuko. He remembers while she sang the lullaby to her, she would also softly pet her head to reassure her everything would be okay.

"Uhh. Miss Tamayo? One more thing. While you sing, if at any point she calms down…use your other hand to…pet her head a bit. I think that may help." He responded.

Tamayo looked confused but she wanted to ease her patient and her brother was the one who knew her the best, so she nodded and trusted his suggestion.

Tamayo then looked down at Nezuko whom did nothing but growl in reaction still not letting her hand go. She looked fierce but also very weak frail and scared. It reminded Tamayo of her on children. Whom sometimes looked pitifully frightened at the silliest things. She was beginning to see her own child in Nezuko. She closed her eyes and softly began the lyrics of the song.

"Hushabye…baby bunny on the hill…"

Tanjiro and Yushiro both looked and listened intuitively as Tamayo began to sing.

"Why is it your ears are so very long…?"

Nezuko was still growling and biting down, but something seemed to have clicked in her.

"Because…when she was expecting me…"

Nezuko looked at the blurry vision and blinked multiple times. The grip on her bite had lessened as she heard something almost familiar.

Tamayo's signing voice was slow and beautiful. It sounded…so warm to Nezuko.

"My mother…ate the leaves from a tall tree…"

Nezuko then gasped. It was coming back to her now.

"…And that is why my ears are so very long…"

The once blurry image that scared her before was starting to turn into a familiar face.

Nezuko slowly lifted her head up, her fangs now leaving Tamayo's hand as she continued to stare at her with a shocked look on her face.

Tamayo assumed this was the cue to start petting her now. She slowly moved her bitten hand away from her and placed her uninjured hand on the little demon girl's head as she continued.

"Hushabye baby bunny on the hill…"

Tamayo slowly began to slowly stroke Nezuko's head as she sung the next few lines.

Tanjiro smiled as he saw Nezuko begin to react and let her hand go. As she was being pet by her caretaker, Nezuko's mouth closed but she couldn't take her gaze off Tamayo.

"…Why is it you your eyes are so very red…"

These words…they're so familiar…where did they…?

The face in the young demon's clouded fever-stricken vision soon revealed itself to be Nezuko's mother.

"Because when she was expecting me…my mother…"

Nezuko finally realizes who this is. Tears begin to form in her eyes and a few hiccups escape her mouth.

"…Ate the red berries from a tree…"

The hiccups then turned into light starts of sobbing.

"…and that is why my eyes are so very red…"

Nezuko saw a faded memory play in her head. She was lying in a futon bed on the floor with this woman sitting beside her. Singing the same song as she laid on her lap. Then she heard words barely echo in her mind.

"M…om…y…'m…s…c…ar…d"

This distorted voice…was it…hers…?

After the memory faded away from her vision, Nezuko began to wail. Tears coming from her eyes she cried loudly. Almost screaming. She buries her head in her arms as she cries in the sheets of the bed.

Tamayo couldn't continue as this shocked everyone in the room. Tanjiro and Yushiro were also frozen in shock. Nezuko was crying. She hasn't cried like this since before she became a demon. Was it the pain from her illness or could it be… did Tamayo's lullaby reach her?

Tanjiro remembers that she cried a little in her sleep upon hearing the lullaby from him on the night she first got sick. This song. It really means a lot to her even as a demon.

Tamayo tried to calm Nezuko placing her hand to her shoulder.

"Oh Nezuko…it's okay I didn't mean to…"

Then Nezuko did something surprising.

Upon feeling this woman touch her shoulder, Nezuko lunged herself into Tamayo's arms and embraces her body tightly. Still crying loudly nuzzling her face into her chest. She was like a scared child wanting her mother's support.

Tamayo was stunned, Tanjiro lightly smiled and Yushiro of course looked aggravated and jealous of the sight he saw before him.

Tamayo then remembered her own children and instinctively returned the hug and began to softly pet her had and use her other hand to pat her back.

"Sssh… There, there little one… It'll be okay…" she quietly cooed to the crying girl.

Nezuko's crying continued for a while until she eventually falls into a deep much needed slumber in the doctor's arms as she finished singing the rest of the lullaby to her.

Nezuko was now lightly snoring as she continued to cling to Tamayo's kimono.

Tanjiro waked over to Tamayo still smiling.

"I knew it." He quietly said.

"Knew what?" Tamayo asked looking to him still cradling his sister.

"Nezuko saw you as more than just family…" Tanjiro said. "I think…she sees you…like our mother."

"Nezuko…" Tamayo quietly responded looking down at her.

"You look a bit like her." Tanjiro said. "She has black hair and purple eyes like you do. So, it's probably not surprising that she'd see you as our mother in her own clouded vision and memories."

Tamayo began to feel herself begin to tear up just like when Nezuko hugged her the first time. First, she sees a monster like her as her as family, but now she sees her as a mother. Thinking back to her past life, it was too much for Tamayo to handle. She buries her face in the young demon's long black and orange locks of hair silently crying. She felt closer to Nezuko than ever after this. Seeing her like her own child even.

"Thank you…Nezuko…" she said quietly smiling and still hugging her.

Nezuko hummed quietly in response.

Chapter 15 is done! Just what the doctor ordered! Or...sang? Poor Nezuko really misses her mom... :(

Also I apologize about the inconsistency of the song lyrics. I wrote the chapter "Melody of the Past" based on a poorly translated manga while this one I wrote after Season 2 of the anime finished coming out.