Yoriichi's Reincarnation in Tanjiro

The Sun Hashira

(Just a quick note before we begin. I'm aware that in canon, Shinjuro tore up the sun breathing book. But, I have a headcanon that he only did that after Rengoku died. So, since Rengoku didn't die, the book is still intact in its original form. Try to bear with me for the deviances from the canon story. Also, keep in mind there are manga spoilers below. Also sorry if this chapter is really boring. It's a lot of backstory)

After taking a quick bath he walked back into his room not wearing his corps uniform anymore and instead wearing the comfortable medical gown he was given to wear in the butterfly mansion. He slid into bed and opened the book. He turned to the first page and started reading.

Alright. Let's see what this book has to say.

'The Guide To Sun Breathing'

First page:
'My name is Yoriichi Tsugikuni. I was born in the Sengoku era. My life isn't something to be admired about, but I suppose I should provide a summary of my adventures. I was born with a mark on my forehead that gave me extraordinary abilities but also made me an outcast in my family. I was an unwanted child so I left my house soon after my mother died of illness. I was supposed to become a priest, but I did not go to the temple. Instead, I wanted to run as hard as I could. Under the infinite expanse of the beautiful sky. And yet, after a whole day and night, I did not stop from exhaustion. In the mountains, I found myself in a small rice paddy among other fields. Someone was standing there. It was a girl about my age. She was holding a bucket and she didn't move for a long time. So I asked her what she was doing. She said her family died in a plague and she was very lonely. So she was going to take home tadpoles with her. And then she stood still again. But as the sun began to set, she freed the tadpoles from her bucket. I asked why she had freed them. She said she felt bad for separating them from their families. I then offered to come home with her. She turned around crying. Her eyes were like obsidian. The girl's name was Uta. We decided to live together. Uta had a habit of talking from morning until evening. Thanks to her, I learned that people see the world in different ways than I do. She had never heard of seeing through living bodies as if they were transparent. Then I understood why I always felt vaguely estranged from other people.'

Second page:
'Ten years later, we married and it was nearly time for her to give birth. In preparation, I set out to summon a midwife. I planned to return before the sun set. Along the way, three mountains over from where we lived, I met an old man traveling. Even though he had a bad heart, he was rushing to visit his son, who had been fatally injured in battle. I delivered the old man to his son and decided to summon the midwife the next day. I hurried toward home as night fell. But by the time I arrived, someone had killed both Uta and the child in her womb. For ten days, I was in a daze as I cradled her body. Until a swordsman came in pursuit of a demon and encouraged me to mourn them properly through prayer. 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 faces of my beloved 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. So I became a demon slayer.'

Third page:
'I created the Sun Breathing style, the original and the breathing style that all other breathing styles derive from. There had always been those who hunted demons but none used breathing. So I taught them. The swordsmen called hashira were already superior. And when they used breathing along with the original sword forms of flame, wind, water, thunder, and stone, they improved even further. The demon slayers defeated demons one after the other. When demons killed my twin brother's subordinate, he too became a demon slayer and lent us his strength. Soon after, I found the demon's progenitor. And in that moment, I knew that I had been born for the purpose of defeating Muzan Kibutsuji. This unworthy man of power had seven hearts and five brains. And in that moment, I completed my sword forms.'