The warrior Muzan feared was a swordsman named Yoriichi Tsugikuni. Yoriichi was the only slayer before Tanjiro who came close to killing Muzan, and the flashback of their fight occurred in Chapter 187.
1) Yoriichi Tsugikuni
Yoriichi was born with the Demon Slayer mark and prowess in swordsmanship. His powers were beyond comparison as he defeated Muzan once and had him on the verge of death until he managed to escape.
Yoriichi Tsugikuni, the first swordsmen to ever use Breathing Styles, once nearly killed Muzan with Sun-Breathing, and Muzan has been both physically and psychologically scarred ever since.
Yoriichi combined all his forms into one strike and turned his blade bright red, enabling him to cut through all of Muzan's weaknesses and overpower him.
This medicine was created by both Shinobu and Tamayo. Following this, Gyomei Himejima, Sanemi, Giyu Tomioka, Obanai Iguro, Mitsuri, Tanjiro, Zenitsu and Inosuke attempted to behead Kibutsuji Muzan. Ultimately, Muzan transformed into a baby-like form and tried finding shade to escape the effects of the sun.
Yoriichi's mastery of the Sun Breathing technique, combined with his incredible speed and agility, made him a formidable opponent for Muzan.
With his blood, Muzan can turn others into demons and seems like an unstoppable foe. However, the demon king seems to fear one thing: Tanjirou's hanafuda earrings. A look into Muzan's past reveals that only one man ever came close to killing him.
Don't go! DON'T LEAVE ME HERE! Muzan speaks his final words as he loses control over Tanjiro.
In conclusion, Tanjiro will not be able to kill Muzan by himself since the Demon King is far superior in every aspect of combat. The manga has shown fans the singular way that Muzan could be bested and it was only due to the collective efforts of Demon Slayer Corps members.
Yoriichi lived till old age, likely due to him having been born with the mark and thereby avoiding the curse altogether. Gyomei on the other hand did not activate his Mark until he was already older than 25. It was speculated that when he awoke his Mark during battle that he would likely die within hours.
But if we are talking about the human form, then it's a big fat NO, because Tanjiro has just mastered the Sun Breathing whereas Yoriichi is the inventor of it, also he's way more powerful and holds an unfathomable battle intellect, larger than any Demon Slayer in history, so in conclusion, no one is remotely close to ...
The two known demons who broke free of Muzan's curse are Tamayo and Nezuko. Tamayo was able to break free of the condemnation when Yoriichi fought Muzan, nearly killing him in the process.
In a nutshell, Muzan, being the progenitor of demons, is not scared of Doma. However, he is irritated by his inability to decipher Doma's thoughts and feelings, which is the ultimate control he has over all of his creations. Upper-Rank Two: Doma is a nihilistic maniac and a misanthropic cold-blooded demon.
However, the thirteenth form is the one that would land the final blow on Muzan. This form is a repetition of every Sun Breathing form performed in succession that would kill Muzan by hurting all of his vital organs.
After various battles within the Dimensional Infinity Fortress the remaining Upper Moons are killed by the hands of various Demon Slayers. The last member, Upper Moon Four Nakime, ends up being killed by Muzan Kibutsuji himself to stop the Dimensional Infinity Fortress from being controlled by his enemies.
Many Kimetsu no Yaiba fans deduce that Yoriichi is Tanjiro's father, but that isn't the case. However, Yoriichi is responsible for teaching Tanjiro's ancestors the Hinokami Kagura, which has been passed down for generations.
Three Hashiras Tanjiro could beat in Demon Slayer
Comparing an end-of-story Tanjiro to an end-of-story Muichiro, Tanjiro likely takes the win home 99 times out of 100.
As the battle reached its climax, Tanjiro was able to knock the doll's head off and discovered that the mechanical body contained a mysterious sword. Fans of the manga will recognize this sword as the one carried by Yoriichi Tsugikuni himself.
Muichiro Tokito – Mist Hashira
In direct combat, he easily overpowered our protagonist Tanjiro so his strength is not to be taken lightly. Another testament to his skills is his win over Gyokko, an Upper Rank Five demon, whom he defeated all by himself – too with ease.
After he neutralizes Tamayo's poison and emerges from his flesh cocoon, Muzan's hair grows in length and turns white due to Shinobu's poison accelerating his age. He also grows numerous mouths all over his limbs, each one lined with a set of incredibly sharp fangs.
Moreover, while she was asleep, Urokodaki performed a unique hypnotism on Nezuko, making her believe that all humans are her family and she must not hurt them in any way. With her immense fondness for humanity, Nezuko broke out of Muzan's control, becoming free to do anything at her will.
We first see Doma when he is still the Upper Moon Six while he is in the middle of eating a geisha. Later he becomes even stronger and rises to the position of Upper Moon Two. He dies because of the lethal amount of poison he absorbed through Shinobu Kocho's body followed by Kanao Tsuyuri beheading him.
Does Muzan have a favorite demon? Despite the fact that Muzan. is always shown to have disdain for his creations, Muzan does in fact have a favorite. On that list is Naki, made due to a convenient blood demon.
Thus, Muzan created demons for hundreds of years even when he didn't want to turn someone. Since he didn't know anything about the Blue Spider Lily medicine, he needed others to find the plant for him by happenstance. This is the general reason why Muzan turned Nezuko into a demon.
Moreover, Tanjiro's appearance somewhat resembled Tsugikuni. So the only reason Muzan is afraid of Tanjiro is because of the Hanafuda earrings he possesses, which acted as a reminder of his downfall.