Demon Slayer Backstory's (Cannon)

Yoriichi Tsugikuni

Word count : 2,191

This is a really long backstory

Yoriichi and Michikatsu (Kokushibo) are identical twin brothers, their birth date is unknown however it is known they were born in the middle of the Sengoku period.
The twins were born to a high-ranking family causing strife to shift through them. All because Twins were thought to be troublesome in choosing who the heir to the family was. But in this case, it was an easy choice because Yoriichi was born with a very noticeable birthmark on his forehead. This caused Michikatsu to be chosen to be the heir and their father announced that Yoriichi would be killed. However, the Mother who was named Akeno went into a rage only a mother protecting her child could produce. Soon after Akeno raged the twin's father relented and allowed Yoriichi to live only under the condition that Yoriichi would be sent to a monk temple at the age of 10. 

Growing up it became obvious that one thing no one other than Yoriichi knew was that the mark that he was born with, (which was considered unlucky by most people) actually granted him incredible physical prowess and the ability to see the bodies of living things in transparency. Because of this ability, Yoriichi was able to see that his mother was not well, he saw how it weakened her left side, so Yoriichi frequently attempted to support her and help her move around. As he stayed at Akeno's side he never said a single thing causing the whole family to believe he was mute. So Akeno made a pair of Hanafuda charm earrings in the hopes the gods would bless him with the ability to speak. Every day Michikatsu watched his brother with pity, all because he saw his brother clinging to his mother, never saying a word. He always assumed his brother was weak and that's why he clung to their mother, but that wasn't his fault, no one else had any idea she was dying, they always thought Yoriichi was the weak one.

The twins grew up separated, however, Michikatsu snuck away to see Yoriichi. This continued even after the father caught the two together, Michikatsu just wanted to see his brother. So he started sneaking out at night and walking to Yoriichi's little cabin. One of these nights Michikatsu gave Yoriichi a little handmade flute in an attempt to comfort his younger brother. Yoriichi saw the meaning and held the flute to his chest and quietly promising his brother he would always have it on him. 

When Yoriichi was seven he saw his brother practicing as usual, he decided to become the second-best swordsman in the world. Michikatsu noticed his brother and took a small break to talk to him. It was that day Yoriichi spoke for the very first time in his life, he told his brother his plan to become the second-best swordsman. This surprised Michikatsu very much, mainly because for the first time ever speaking Yoriichi spoke with a clarity of a fully grown man. His voice was soothing and calm, with not an ounce of strain in it. As Michikatsu stared at his brother in shock Yoriichi smiled for the first time in his life and walked away. Still, one of their father's men tasked with training Michikatsu heard Yoriichi's declaration and decided to humor Yoriichi, showing him a simple stance. Yoriichi took note of everything and followed the instructions getting everything perfect. The teacher praised Yoriichi and told him to try to strike him. Unexpectedly, the young boy flew into action and landed four blows against the man, shocking his brother, who despite his training had never landed one. However, immediately after striking the man unconscious Yoriichi decided he never wanted to use a sword again. His only reasoning was that he hated the feeling of hitting someone and renounced his goal to become a samurai. Michikatsu often asked him about how he managed to hit the man and Yoriichi described what was likely an early form of a Breathing Style. 

The day the twin's mother died Yoriichi went to Michikatsu's room at night to tell his brother the news and bid farewell, planning to leave for the temple that night. He expressed gratitude towards his brother, stating that he would always keep him in mind and fondly tucked away the flute Michikatsu had made for him earlier. It was later revealed to Michikatsu through their mother's diary that Yoriichi had known everything about their mother's illness. It was also revealed that Yoriichi knew about their father's plan at making Yoriichi the family Heir and sending Michikatsu to the temple. Because he knew of this plan Yoriichi left sparing his brother for the life of a monk. Despite this kind act, Michikatsu developed an intense hatred and envy of Yoriichi for continuing to surpass him in everything and continually showing gratitude to gain seemingly nothing. He believed his brother to be a fool for leaving and sparing him.