In this world Tanjiro's family practically forced him to stay home, this is my interpretation of what would have happened if Tanjiro would have also been turned into a demon along with his sister.
I do not own demonslayer
Tanjiro opened the door to find a tall man dressed in a jet black suit with white undergarments and a red tie. His eyes were a pale red that was not quite pink with slitted pupils like a cat's. Tanjiro gave a bright smile and opened his mouth to greet the man. Just then a strong gust of wind blew in the door and the smell hit him in full force. It was like Sulfur and oil that had been sitting in the sun for days. The sheer force of it made Tanjiro stop mid-sentence
"Hello! My name is Tanjiro Kamado It's nice to-" He stopped as he fell into a coughing fit before regaining his composure and finishing his sentence. "-meet you, what brings you here?" The tall dark man seemed to stare at something just over his shoulder before snapping back to himself and responding.
"Hello Tanjiro Kamado, My Name is Muzan Kibutsuji and I have business with your family". Muzan Kibutsiji, the name sent a shiver down Tanjiro's spine, something felt off about this man. His eyes, the smell, were somehow very unsettling. He tried to shake it off and be freindly to the stranger.
"well" Tanjiro replied his voice breaking slightly before trying again. "Well my family sells charcoal. If you need some, we've got plenty. I was going to go down the mountain to sell some today but my family convinced me to stay home."
"A wise choice." Muzan said "It's getting colder every minute but unfortunately my travels here are not charcoal related."
At that moment Tanjiro's mother Kie also appeared in the doorway.
"Tanjiro?" she asked with a loving tousle of his hair "Who is this?"
"Oh, this is Muzan Kibutsiji" Tanjiro answered "He says he has some business with our family"
"Well dont just stand there in the cold, come in! Kie said.
As Muzan entered the house, Tanjiro felt slightly embarrassed, he and his mother always kept the house perfectly clean, but it was falling into disrepair with some parts of the walls and ceiling being hastily replaced with spare bits of wood. His mother on the other hand led the stranger confidently to the sitting room where all of his Siblings were playing. Most of them sat on the ground wrestling while Nezuko sat mending her kimono with a sleeping Rokuta in her lap. The moment the strange man sat down, the door slammed shut. Everyone looked up at the noise. There was Silence for a moment before Kibutsuji broke it by saying.
"Now I believe I said we had some business to attend to, but first-" The man stalked over to Kie and snarled "I dont need you, you are not one of his descendants, you are useless." Then he snapped head clean off, as easily as though she were a carrot. The children stared at the mutilated body of their mother's corpse, stunned.
Takeo was the first to respond, he shouted.
"Our mother is the most amazing woman on the planet! HOW DARE YOU SAY SHE IS USELESS!" Takeo was wildly swinging the axe they used to chop wood that he'd grabbed off of the wall. Kibutsuji easily dodged then picked him up and examined him.
"You are the descendants of the one swordsman who has ever come close to beating me, you are the last surviving line of the sun breathing technique" Tanjiro's head was spinning, his mother was dead and he was trying to wrap his mind around what this intruder was telling them. But it didn't make any sense!
"I hope that once the demonification process is complete; one of you will someday be able to conquer the sun."
Tanjiro couldn't put it together, Demonification? Sun Breathing? Conquering the sun? None of it made any sense and his mind was still in shock from loosing his mother. But he came crashing back to reality when Kibutsuji's nail seemed to grow longer. In an instant, he cut a long gash in Takeo's chest. Takeo began to convulse in his arms, this went on for what seemed like hours before Takeo coughed up some blood and went limp in his arms with one final gasp. Muzan cursed in anger, raked his clawes over Takeo's body and threw him into the wall, leaving a streak of blood leading to where Takeo finally lay.
Muzan started muttering to himself "That was barely any blood, Ive never seen one so weak to its effects, It could be because of his age but no, the sun in him must reject the blood, making it impossible for him to turn into a demon." He suddenly got a worried look on his face "What if all of them are like that?"
Tanjiro was still frozen, watching in a Trancelike state while Muzan was muttering. This couldn't keep happening. First his Mother and now Takeo. What else would this man do? No, this couldn't be a man, he flashed back to the stories his grandmother had told him about man-eating-demons. This had to be what she was talking about. Tanjiro took a step towards Muzan but just as he did Nezuko ran past carrying a crying Rokuta and dragging along a terrified Hanako. She yelled at him.
"COME ON TANJIRO WE HAVE TO RUN!"
"I dont think so" said Muzan, In the blink of an eye he made three scratch marks on the back of Nezuko's neck. She immediately started convulsing on the ground just as Takeo had but she lasted much longer before eventually going limp.
"Hmm promising, but not as good as I had hoped, perhaps age IS a bigger part of the equation than I realized" Muzan said to himself, turning to Tanjiro as he said it. This finally, is what really brought Tanjiro back to himself. He realized that at some point he had fallen to his knees. He pulled himself to his feet and stood in between Nezuko's Body, his two remaining living siblings and the Demon.
"You wont lay a FINGER on them!" Tanjiro yelled.
"Oh, wont I? The demon replied and in half an instant he had Tanjiro pinned up against the wall with one arm, while the other extended one finger towards his forehead. The Demon found the vein in the middle of Tanjiro's forehead. Pushed his finger forward gritting his teeth slightly as he struggled to get his finger into Tanjiro's rock hard forehead Tanjiro noticed his Distinctly sharp canine teeth. After a moment it broke the skin and Tanjiro felt something foreign enter his brain, a thick cold oily substance that felt odd for a moment, then sank into his bloodstream. Then the pain began.
The room spun, Tanjiro's body started twitching, as though he were having a violent seizure. He fell to the ground as Kibutsuji removed his arm. He was on his knees Holding his vibrating head coughing up blood. Wishing for it all to stop. Two forces seemed to be fighting for control of his body, Tanjiro used the last of his energy to look up through a red haze of pain to see a triumphant look on Muzan Kibusuji's face. Finally his brain gave out and everything went dark.
The first thing Tanjiro knew when he awoke was that he was hungry. So Incredibly hungry. He didn't know who he was, where he was or how he got there. Slowly he lifted his head from the ground. He was in a small room with the dying embers of a fire in a hearth. There was hardly any light but Tanjiro could see fine. He stopped wondering where he was though when he saw the bodies.
His weak legs wouldn't support him, so he crawled along towards the nearest body. It didnt have a head and it was covered in blood, but he didn't care. He grabbed the woman and almost desperately bit into her calf. In no time the leg was gone. He was still hungry and as Tanjiro began to gnaw on the second leg, the hunger pain eased and his mind became a bit more clear. Something felt off but he couldn't figure out what. The smell of blood was working on his brain like alcohol and making it hard to think. Trying to shove these thoughts away he reached for the smallest body, yanking it towards him. He bit down hard on the tiny child's hand feeling the fragile bones break easily in his powerful jaws. How could something so pitiful deserve this.
Then It all came crashing back, his name, his life, his family and all the tragic circumstances that had led him here. He spit the bones of Rokuta's hands out, now sucked dry. Tanjiro could barely hold himself together, he was crying. His whole face was a mess of tears and snot and his families blood. Tanjiro was crying holding Rokuta and what remained of his mother's body in his arms.
He did not know how long he sat there before he heard a creak and a moan. Tanjiro whipped around to see Nezuko standing there, blood soaking through her pink kimono. Her hair was down and the ends seemed to be tinted orange in a way he had never noticed before.
"Nezuko!" He cried "Nezuko you are alive! I'm so glad!" Tanjiro ran forward to embrace her but then she jerked her head upright and stared at him.
Her eyes, they were pink with slits for pupils. She noticed the blood around his mouth became extremely angry and charged him.
"Nezuko, What are you doing?" Asked Tanjiro as she took another step closer. Upon realizing that Tanjiro was not going to fight she lunged towards Takeo's body. Before she got there, Tanjiro tackled her from behind and yelled:
"Nezuko, I love you, I don't know what's going on, I wanted to eat our family too and I don't know why! So please don't do this don't make my mistakes. I love you!" His desperate pleas fell on deaf ears. While Nezuko was growing ever closer to Takeo. "Forgive me Nezuko, he said before whipping his head back and head-butting her from behind. Her body went limp and they fell in a heap on the floor.
