Prologue:Twilight of a swordsman

Over the years there were countless legends, that count astonishing events,describe the power of mythological creatures or the heroic deed of a historical character. Some of these almost look like something taken out of a fairy tale or of the wild imagination of a child.

One of these stories is that of some nocturnal creatures with an inhumane strength,overdeveloped senses,supernatural powers and an insatiable hunger for human meat,demons,was the name for which they were known.However,even if these creatures look invencible for any mortal,there was some people,who promised to protect the innocents from these these monsters,the demon slayer corps. Among this group there was one with a skill and ability so superior that they would be given by the gods themselves. Few people who claimed to have seen him described him as the personificación of the sun in the earth and that's why even the demon king was scared to face him in a battle.

Nobody couldn't confirm if this story is real or not but all people agree that if someone owned such power,he or she would be the most fortunate person in the world…except one.

Yoriichi Tsugikuni has always considered himself as a worthless man,with a life full of terrible disappointment and deception.He lost everything he cared about,from his mother to his wife.

-My dream was to live a quiet life with my family in a small house where we would sleep side by side. I would be close enough to see the beloved faces of my wife and child and close enough to reach out and take their hands. That would have been enough. But even that did not come true. Demons exist in this beautiful world.-

He had the luck to have an older twin brother,Michikatsu…only to see how he walked away from his life and turned into a monster.He was blessed with a gift like the transparent world…only to see how the body of his own mother deteriorated slowly without nothing that he can do,even if he studied harder medicine and human anatomy to create a cure with the few resources he counted, the death reclaimed her soul. He received an innate ability with the sword…just to fail and be incapable to protect the love of his life. He discovered and created a powerful technique like the sun breathing and with it,the possibility to eradicate the demon's tyranny…just to let him escape,Muzan Kibutsuji,the father of the demons.

This last one frustrated him at most. The first time he was face to face with muzan,Yoriichi realized that he came to this world and got all his gift and abilities only to eliminate the demon king,it was his goal,his destiny and he couldn't comply with it,and the consequence was all life that were lost by the hunger of the demons.

Yoriichi always wondered why,of all the people that existed and to exist,HE!!! was the chosen one to deal with this responsibility. A good doctor could have used the transparent world to heal many people from the worst illness or injuries,maybe even heal his mother.His brother could have used his ability with the sword to become the best samurai in history,like he wished. A demon slayer with the sun breathing definitely could have defeated Muzan without a doubt.

-Rengoku at least wouldn't have stopped until left nothing but ashes-thought Yoriichi bitterly

Despite being fired from the corps,Yoriichi kept a good friendship with Rengoku,helping him to improve the flame breathing,and in return Yoriichi received information about dangerous demons to chase the fire breathing but even with Rengoku's exceptional technique,he wasn't able to recreate the sun breathing.Nevertheless,Yoriichi made sure that the breathing doesn't die with him.Rengoku wrote all the information about it in a diary,so that someday,someone is able to learn it,in addition,Yoriichi taught 12 of 13 forms of the sun breathing to the Kamado family, a family dedicated to the sale of coal. Yoriichi met them when he decided to come back to the home he shared with her deceased wife,Uta,however he was surprised that it was already occupied by said family. Sumiyoshi Kamado,the patriarch of the family,promised that he will teach the techniques to his childrens,under the name of the hinokami Kagura,and this will pass from generation to generation,as a way to honor Yoriichi's memories.This specific memory brought Yoriichi a nostalgic smile,while he was thinking about his old but also best friend. He hadn't seen him in more than 40 years and although he wanted to visit him and his family,he had a mission to complete and distractions were no longer allowed.

Unfortunately,Yorichii's was on the verge of the end,he spent all his life researching without a rest any clue about Muzan Kibutsuji but he found nothing,it was like Muzan disappeared from the reality. However on a bloody moon night,he heard the rumor that a powerful demon was hidden in the tower of an old temple. He wished very much that this demon was Muzan,but the identity of that demon left him a terrible feeling of sadness.

-Impossible…how are you still alive?-exclaimed the demon, surprised and at the same time,angry.

In front of Yoriichi was his old brother Michikazu,but now under a new name,Kokushibou.His body seemed just as young as in his time as a demon slayer, except for the detail of 2 extra pairs of eyes on his face. This horrified the old swordsman, however, if he couldn't finish off with Muzan,at least he was going to free his brother from his curse.

-Brother…-said in a sad tone while some tears started to form in their eyes-this is heartbreaking-.

Despite his impassive facial expresión,Kokushibou felt for the first time in many years a slightly warm feeling in his heart ,leaving him confused.But this confusion disappeared after Yoriichi drew his sword with the intention of cutting his head.

-I have only one opportunity,my body won't resist the adrenaline rush-though with determination

He drew his sword and his frail posture changed into an imposing combat figure.In the blink of an eye,Yoriichi made an almost perfect cut directly to the neck of his opponent,but this"almost"was the problem that prevented the neck from being completely cut. At the last second, many flashbacks of him and his brother together, caused a slight feeling of doubt, as if a part of him did not want to harm his brother, regardless of whether he was a demon.

At the end,the world turned black to Yoriichi,he knew that he failed again,and now he is dead,watching how his soul leaves this world to rest in peace forever.The inconvenient was the fact that he doesn't want to rest,no,he wished desperately a second chance to correct his mistakes,to save the lives he couldn't save when he didn't kill the demon king. He wished for just a happy life.

His soul screamed from the depths of himself, begging for a second chance, wishing to live again, to be able to end with Muzan and enjoy the wonders of the world. He begged with all his might,he didn't know how long he had been begging but suddenly a flash lit up the whole place, blinding Yoriichi for a long time,until it started to disappear,letting him see the place where he was.

It was a humble room with a view of certain mountains familiar to him.It was undoubtedly his old home,and for a second a slight hope sprung from Yoriichi's heart, thinking that his whole story with the demons would be more than just a nightmare, that Uta's death never happened and that now he would had a family to live happily. However,fate didn't lose any second to remind him of his new place in the world.

-Tanjirou!!-notice a childish voice from behind the door-come eat, breakfast is ready!!!-

Those words were enough to turn his hope into confusion before a flood of memories attacked his head and he was left once again in the darkness from whence he came.

A/N:Greetings!! I hope you have enjoyed this prologue. After a long time reading several stories I have decided to create my own, not only to express various crazy ideas in my head, but also to practice and improve my English, so if there is something wrong or something that sounds weird, please let me know. In this story Yoriichi reincarnates directly as Tanjiro, having the memories of both his past life and his current life, it is an idea that I have not seen here, there are variants where Tanjiro is as strong as Yoriichi or reincarnates but without being him directly. I want to do this version with everything that both characters can contribute together. Without a doubt, it will be quite a challenge to level Yoriichi's power to Tanjirou's story, it will also be interesting to see how his knowledge of demons can help change the destiny of someone who another person. Without further ado, I say goodbye, I will try to be able to update at least once a month, and if you have any idea, do not hesitate to share it in comments or by DM. Without further ado, thank you or greatly for your attention :)