Tanjiro's scar is one of the most intriguing parts of his personality. Some believe that it is a birthmark, while others say that it is a result of an accident. There are multiple stories saying that he got it while saving his brother from burning charcoal. However, after the mystery unfolds, it seems that this mark is not a birthmark or a result of an accident. It is only found on the bodies of exceptionally strong Demon Slayers.