Yandere!Demon Slayer x Reader

Chapter Three

Since the day (Y/n) discovered her breathing technique, she has been training day and night, often times she would overdo it and collapse on the ground, Tanjiro would carry her back to the house.
Seeing her in the state she was made him both upset and angry. He didn't want to see her hurt.
"(Y/n)-chan you really don't have to do this much. What if you get sick?"
Tanjiro commented one night while she was meditating and he was observing her.
Sighing, (Y/n) opened her eyes and smiled at him.
"You know I have no other option Tanjiro-kun. It took me a month to master my emotional and physical balance so that I don't hurt myself. And I need to master all the forms so that Urokodaki-sama can send me to the final selection. Takahashi-sama is counting on me to do my best. Also we promised to work together on saving Nezuko-chan. I need to get stronger, after all you can't count on others saving you." (Y/n) finished, getting up from the floor she walked over to her futon and laid down.
"I will go to sleep earlier. Good night Tanjiro-kun, sleep well."
"Good night (Y/n)-chan." They smiled at each other and silence fell over the two.
After Tanjiro was sure she fell asleep, he sat down next to her sleeping form, gazing at the girl's face.
"I will always protect you (Y/n)-chan. You and Nezuko are the only two people who matter to me. I won't lose you, ever. After everything is over I will marry you."
Tanjiro giggled quietly and went to sleep, ready for the next day.

Timeskip

"I have nothing more to teach you two." Urokodaki commented and the sweat dropped.
'A year after (Y/n)-chan and I arrived to Mt Sagiri... Isn't that too soon?' Tanjiro thought, said girl was having similar worries.
'Is he sure this isn't too soon? I am not sure if I have full control over my breathing technique...'

"Whatever happens next is up to the two of you. Now follow me."
The duo followed him till they were in front of two big boulders.

"If you successfully slice them in half, I will allow you to enter the Final selection. Otherwise you won't be qualified."
'Can you even slice this thing in half with a sword?'(Y/n) thought while looking from the boulder to her sword.
"Urokodaki-sama wait!" Her head snapped to the direction of the retrieving man when Tanjiro yelled.
"He really left us alone here..."
"Yeah..."
"Ok! Let's do our best (Y/n)-chan!!"
Tanjiro's determined smile gave the girl determination and she took her sword out.
"Let's!"
They both let out a battle cry and swung their swords at the the boulder, only for the impact to send them to the ground.
'This will be a lot harder...' (Y/n) sweat dropped.

From then on both Kamado and (L/n) were training on different sides of the mountain, perfecting the forms of their techniques.
(Y/n) was currently slicing trees and branches, the animals close by watching her as usually.
'My feet... Wait!' She took off her shoes and sighed in relief.
"Its cold, but its easier to move now."
While she was training, (Y/n) noticed her body endured more and more pain, as well as her eyesight got a lot better.
"The training is paying more and more off! I will show you Takahashi-sama! You will be proud of me!"

Six months passed and both Tanjiro and (Y/n) were running towards their boulders, trying to slice them, but to no avail.
The (h/c) haired girl fell on the ground, both feet and hands bloody but it didn't cause her as much pain as it would a normal person.
'God damn it! Why won't it work?! What am I doing wrong?!'
"Aghhh God damn it!" Tanjiro yelled and out of frustration hit the boulder with his head.
"Are you alright Tanjiro-kun?"
"No! No why won't it slice?! I have been training for so long and now-"
"Enough!"
Tanjiro and (Y/n) looked up from where the voice came, only to find a boy with a salmon colored hair, a fox mask and a geometrical yellow and green kimono.
"Who are you now?" The girl asked, confused as to when he appeared.
"A man shouldn't whine. When you suffer, suffer in silence, just like she did."
The boy told Tanjiro while pointing at (Y/n).
'Great who is this guy now?'
All of a sudden the boy jumped up and charged at (Y/n). Getting up quickly, (Y/n) blocked his attack, but he was too strong for her and she landed on the ground, the boy pointing his sword at her.
"If you are a man, if you call yourself one-"
The boy was cut off by Tanjiro's scream. He pulled away the sword from (Y/n) and blocked his attack.
"(Y/n)-chan is not a man! She is a woman and don't you dare to attack her like that!" Tanjiro yelled in rage, surprisingly both the girl and the masked guy.
"Tanjiro..." She mumbled.
The boy shrugged and pushed Tanjiro to the ground.
"Slow. Week. Pathetic. Immature. That's not what you call a man. You are not ready for anything boy."
Growing angry at his words, (Y/n) took her sword and charged at the salmon colored boy.
He barely had time to block her when she swung her sword again.
"Shut up!"
With a strong swing, (Y/n) opened her eyes only to find the boy gone.
"Huh? Where is he?"
"(Y-Y/n)-chan..." Tanjiro said from behind her.
"What is it? Are you hurt somewhere?" She asked in panic, only to see Tanjiro pointing at something behind her. Turning around, she was shocked to find the boulder sliced in half.
"I... I DID IT! TANJIRO-KUN I DID IT!" (Y/n) cheered and hugged the shorter boy, who returned it with a big blush on his face.
'She is soft... And smells nice too!'
"I see you successfully sliced the thing. But you boy need to still grow into a man." The boy from before commented, sitting on the one undamaged boulder.
'Something is off about him...' Both students thought while looking the boy up and down.