The protagonist of Demon Slayer, Tanjiro Kamado, is easily recognized by the iconic facial scar located just above his eye. But how did Tanjiro get this distinctive scar, and what significance does it have to the story?
From the very first chapter of the popular manga, Tanjiro is shown to have a scar over his eye, so its origins predate the start of Demon Slayer's story. Prior to the beginning of the narrative, Tanjiro lived with his parents, who were charcoal sellers, as well as his brothers and sisters, including Nezuko. One day, as the children were playing, one of them knocked over a burning pot, sending hot coals flying everywhere. Tanjiro tackled his younger brother to get him out of the way, and caught the coal in his face instead, leaving behind the scar he's seen with at the start. It winds up being an appropriate marking, as it's both a symbol of the devotion he has to his family and a tie to the fire element that he'll be increasingly associated with as the series progresses. That isn't quite the end of the story for Tanjiro's scar, however.
Fans may notice that it looks a bit different later in the series than it did earlier on, with the scar's shape and size changing slightly. But these changes are no mere continuity error; it's a direct result of the events in the series. When Tanjiro approaches the end of his training to become a Demon Slayer, he and the other recruits are tasked with defeating a powerful demon as the final selection. Most of the other recruits are killed by this demon, and Tanjiro doesn't escape the battle unscathed, either. The scar is damaged during the fight, and heals rather slowly afterward, becoming a little larger.
Tanjiro's scar serves several different purposes in the story. Firstly, it's a distinctive feature that makes him stand out. While other Demon Slayers can go incognito and blend in with civilians, word of Tanjiro's appearance spreads quickly among the demons, and he's recognized almost instantly by his adversaries from early on. As Tanjiro becomes a greater threat to the demons, the scar grows and becomes more noticeable, rendering him easier to spot. Later in the story, as Tanjiro begins to learn about his father's past, the similar mark he bore, and the Hinokami Kagura (Dance of the Sun God), it's revealed that those who are destined to master the true demon slayer form, known as Sun Breathing, will bear a red birthmark on their face (called the Mark of the Sun). Since demons are destroyed by sunlight, learning to harness the sun's power is the ultimate means to destroy them. The marks grow as the user achieves their fullest power, so Tanjiro's scar changing as the story progresses actually hints at how far he's progressed.
While facial scars have been popular in anime and manga as of late, with characters like My Hero Academia's Shoto Todoroki and Dr. Stone's Senku sporting them, Tanjiro's scar and the usage of scars in Demon Slayer in general prove that these can be more than just distinguishing features. As in Demon Slayer, scars can advance the plot, reveal important character details, and serve to mark a character for something more.