Scars are common in Demon Slayer, but how did Tanjiro get his scar?
Tanjiro got his scar while shielding his brother from a knocked over brazier. These are portable heaters meant for holding lighted coals and warming up food. Tanjiro later developed a Demon Slayer Mark in the same spot, but he got his initial scar from saving his brother.
Rengoku’s father, Jurousan, wrote to Tanjiro in chapter #81. He apologized for his rudeness and offered some insight on Tanjiro’s Sun Breathing capabilities.
Jurousan specified in his letter that the Sun Breath’s chosen users all have the same scar. Red birthmarks on their foreheads. Tanjiro replies with the following explanation:
“This isn’t a birthmark. This is a burn scar I got when I shielded my brother after he knocked down the brazier. Then I wounded it more during the ‘Final Selection’ and that’s how it came to be.”
Chapter #81
Tanjiro then remarks that he remembers being told his father had a slight birthmark on his forehead.
The Significance of How Tanjiro Got His Scar
Even if he wasn’t born with the scar naturally, the wound still appears to grow and change in accordance to Tanjiro’s power.
His first scar was light and thin. Slightly pink, it’s the first iteration we saw at the start of the series. After his training in the ‘Final Selection’, his scar darkened out and grew more throughout Tanjiro’s forehead.
The scar became a Demon Slayer Mark. These marks can be acquired from birth or unlocked at a later date. It would appear that Tanjiro got his scar naturally from the brazier burning, but his Demon Slayer Mark filled out over the same spot and combined the two scars.
Tanjiro’s scar transformed in color and size after defeating Rui using Sun Breathing techniques. The scar also changed further down the length of the story as his power and fighting capabilities expanded.
Tanjiro got his scar from shielding his brother from a burning brazier. He naturally developed a Demon Slayer Mark in the same spot, but the initial scar was created from the burn of the kettle.