He wasn't just some guy with a sword. Honestly, if you look at the lore of Koyoharu Gotouge’s Demon Slayer: Kimetsu no Yaiba, Yoriichi Tsugikuni basically breaks the entire power scale of the universe before the story even starts. People often confuse "First Demon Slayer" with the founder of the Corps, but the organization existed before him. He was the first to bring Sun Breathing—the source of everything else—into the fray.
Without Yoriichi, Muzan Kibutsuji would have probably won centuries ago. It's a weird thought.
Imagine being born so naturally gifted that the "Transparent World" and the "Selfless State" are just your default settings. Most slayers spend decades bleeding and sweating to reach a fraction of that power. Yoriichi was born with the Demon Slayer Mark. He didn't have to "activate" it; it was just part of his skin. Because of this, he’s the undisputed peak of the series. Even centuries later, Tanjiro and the Hashira are essentially just trying to rediscover the crumbs he left behind.
The Tragedy of the Sun Breather
Most fans focus on his fight with Muzan. But the real story of the first demon slayer is actually pretty depressing. He didn't want to be a warrior. He was a quiet kid who thought his brother, Michikatsu, was the one who was actually talented. He even left home to ensure his brother could inherit the family's prestige.
Life had other plans.
After his pregnant wife, Uta, was killed by a demon, Yoriichi’s path was set. It wasn't about glory. It was about a deep, quiet grief that lasted for nearly eighty years. When he eventually joined the Demon Slayer Corps, he realized that nobody else could use his Sun Breathing. Their lungs literally couldn't handle it. So, he adapted. He taught them variations—Water, Flame, Wind, Stone, and Thunder. These "derived" styles are the only reason the Corps survived, yet they are all just diluted versions of what Yoriichi could do naturally.
Why Muzan Is Still Terrified of Him
Muzan Kibutsuji is an egomaniac. He views himself as a natural disaster, something beyond human reach. Then he met Yoriichi.
In their single encounter, Yoriichi didn't just win; he dismantled Muzan. He saw through Muzan’s multiple hearts and brains instantly. He swung his blade once. Muzan was so traumatized by the speed and the searing heat of the bright red Nichirin sword that he spent the next several hundred years hiding in the shadows, waiting for everyone who knew Sun Breathing to die off.
That’s the level we’re talking about here.
Muzan literally has PTSD from one interaction. He killed off anyone who even wore Hanafuda earrings because they reminded him of the man who almost turned him into ash. It’s also worth noting that Yoriichi lived past the age of 80. This is a massive anomaly. Typically, those who awaken the Demon Slayer Mark die by 25. Yoriichi was so biologically superior that the curse of the mark simply didn't apply to him. He died on his feet, in the middle of a killing blow against his brother-turned-demon, Kokushibo. He died of old age, not the battle.
The Legacy of the Hinokami Kagura
How did the first demon slayer’s techniques survive if he had no heirs? It comes down to a promise and a dance.
Yoriichi befriended Sumiyoshi, an ancestor of Tanjiro Kamado. Because Sumiyoshi realized the weight of Yoriichi’s loneliness and the value of his skill, he memorized Yoriichi’s movements. This became the Hinokami Kagura. It wasn't passed down as a martial art but as a ritual dance. This is a brilliant piece of writing by Gotouge. It explains how a breathing style that was "lost" managed to hide in plain sight for hundreds of years.
- Sun Breathing: The original, most physically taxing form.
- The Mark: Yoriichi was the origin point for the marks appearing on other slayers.
- The Red Blade: He discovered that gripping the sword with immense strength could hamper demon regeneration.
People sometimes argue that Tanjiro surpasses him by the end of the manga. Respectfully, no. Even in the final battle, a poisoned, weakened Muzan is struggling against the entire Corps. Yoriichi faced a prime Muzan alone and finished the job in seconds. The difference is staggering.
Correcting the "First Slayer" Misconceptions
A lot of people think Yoriichi started the Corps. He didn't. The Corps was already hunting demons, they were just really bad at it. They used basic swordsmanship and died constantly. Yoriichi was the "Golden Age" catalyst. He turned a group of desperate swordsmen into a disciplined force of Breathing Style users.
Another misconception involves his brother, Kokushibo (Upper Moon One). Some think Yoriichi failed because he didn't kill his brother. But if you look at their final stand, Yoriichi had already won. He died of a heart attack mid-swing because his body simply ran out of time, not because Michikatsu was better. Michikatsu spent 400 years eating humans and honing his craft, and he still couldn't touch an 80-year-old man who was technically "human."
Actionable Insights for Fans and Lore Buffs
If you're trying to piece together the timeline or understand the power ceiling of the series, keep these points in mind:
- Watch the Earrings: The Hanafuda earrings are the primary visual link between Yoriichi and the Kamado family. They signify the passing of the "Will of Fire" (wrong series, but the sentiment fits).
- Understand the Mark: The Mark is a trade-off. It grants power for a shortened life. Yoriichi is the only exception to this rule in recorded history.
- The Red Sword: Pay attention to how the modern Hashira turn their blades red (clashing blades, friction, etc.). Yoriichi did it purely through his own grip and internal heat.
- The Black Blade: Tanjiro’s blade is black, which is rare. It’s hinted that black blades belong to those who use Sun Breathing but haven't mastered it, or whose talent is so vast it encompasses all colors. Yoriichi's blade also turned obsidian black before it turned bright red in combat.
The story of the first demon slayer is one of perfection in a world of flaws. He was a man who had everything—the power of a god—but only wanted a simple life with his family. He failed to kill Muzan, failed to save his brother, and died feeling like a failure. Yet, his mere existence provided the tools necessary for the next generation to finally end the night.
To dive deeper into the specific forms of Sun Breathing, you should revisit Chapter 192 of the manga, where the connection between the dance and the combat forms is explicitly detailed. Understanding the "Thirteenth Form" is the key to seeing how Yoriichi intended to finish the job he started five centuries ago.
