It is also noted that Tanjiro's father, who taught him the various forms of Sun-Breathing, was born with a scar on his head.
He was born with a mark on his forehead. Tanjuro also wore a similar outfit to his son, sporting a black checkered Haori that was orange instead of dark turquoise.
Despite not being a key character in Demon Slayer, Tanjuro had an important part in Tanjiro's life. Tanjuro was proven to be a remarkably powerful person, despite not being a demon slayer and having a sad sickness that renders his body terribly feeble.
In the show, Tanjiro's father Tanjuro is shown with the exact same head "scar" as his son - and it seems unlikely that the explanation for this is that they both had the exact same scarring incident with a boiling hot kettle. As such, it's clear this is an inherited trait, and not the result of an unfortunate accident.
Yoriichi is the progenitor of Breathing Styles, born with a demon slayer mark, which means he never had to go under special training to awaken it. He was the user of the Sun Breathing Style and the first swordsman to ever use the breathing style.
Gyomei and His Unusual Situation
Only two Slayers were ever known to be older than 25 with a Mark. 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.
They fought demons and trained together, yet Inosuke never acquired a mark of his own. Inosuke did learn a great deal about his tragic past, but he didn't get as much of a chance to shine as his other friends when it came to displaying his talents.
Without the image of his father's dance burned deep inside his memory, Tanjiro won't be able to use the technique that will be crucial in the effort of defeating Muzan Kibutsuji. Other than the Hinokami Kagura, other techniques that Tanjiro learned from his father are the Transparent World and the Selfless State.
So, not only could Tanjuro use his mastery of the Hinokami Kagura for his dance, but he was also an excellent warrior despite his poor health. Tanjuro Kamado bore a mark on his head similar to Tanjiro's own scar, identifying Tanjuro as a chosen wielder of Sun-Breathing.
Tanjiro's ancestor was a good friend of Yoriichi and arguably was one of his only true friends. Therefore Yoriichi gave the earrings as a gift, and since then they have been passed down the generations until they reached Tanjiro.
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.
The divine nature of sun breathing: Tanjiro's link to Yoriichi. The flashback also reveals that Yoriichi had a twin brother named Michikatsu Tsugikuni, who became a Demon Slayer but later turned into a demon and became Upper Moon One, Kokushibo.
Tanjiro and his father look extremely similar to each other. Fans think that Tanjiro was related to the legendary swordsman since he had the same earrings, and their appearances are similar as well. However, Tanjiro is not a descendant of Yoriichi Tsukiguni.
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.
Yoriichi proved to be the most powerful because he one-shot the otherwise strongest being in the series, Muzan Kibutsuji, with absolutely no difficulty.
The black blade represents the Sun and is surrounded by prejudice and misconceptions, as historically every demon slayer who held it lived a short life. This could mean that Tanjirou is destined to break the pattern and set a new legend for black Nichirin blades in the Demon Slayer universe.
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.
Long forgotten and unknown to most of the Hashira during Demon Slayer's narrative, the technique was kept alive by members of the Kamado family, and passed down from father to son as a ceremonial dance performed every New Year.
We know that Tanjiro was able to completely outclass Akaza for a few minutes due to his access to the Selfless State and the Transparent World. It was in this flashback when fans realized that Tanjiro was able to learn this because of his father.
Conclusion: Kokushibo, the upper moon rank 1 demon and Yoriichi are not Tanjiros' father and neither are Tanjiro's relatives. However, Kokushibo and Yoriichi are siblings and respect each other a lot despite Kokushibo hating the entirety of his brothers' being.
It turns out that Muzan attacked the Kamado family and specifically turned Nezuko into a demon in an attempt to create a demon that would be able to withstand being in the sunlight.
The Wind Hashira has one of the saddest backstories in Demon Slayer. His mother had turned into a demon and had killed five of his siblings. He was forced to kill his own mother in an attempt to save his only remaining brother, Genya.
Demon Slayers who have awakened the Demon Slayer Mark are said to die upon reaching the age of 25. Michikatsu Tsugikuni speculated this to be because the mark exchanged the life span of its user for power.
Plot reasons, I'd say. Rengoku died before the Mark was introduced into the story. Similarly, Tengen was jacked up during the Entertainment District mission and retired immediately after. As he wasn't on the front lines anymore, he never had the chance.