Demon Slayer Kimetsu no Yaiba is already set deeply into the Entertainment District arc, keeping fans on the edge of their seats with exciting battle scenes and memorable revelations regarding some questions the fandom had since the beginning of the series – like the origin of Tanjiro’s scar. Another question that emerges amidst the Demon Slayer fandom is the reason why Tanjiro’s Nichirin sword turned black when Tanjiro held it for the first time, which is back in season 1.
In Demon Slayer, Nichirin sword shows the personality of the wielder by changing colors, and Tanjiro’s was unexpectedly black to everyone’s surprise. Tanjiro is a kind soul that feels sorry even for demons he has to slay, and he does kill only to protect others. He is selfless, brave, and a great human being, so why did his sword turn black? Demon Slayer is not the first anime to use such symbolism for the purpose of overshadowing or defining characters.
Black swords in anime usually belong to orphaned characters who are often loner wolves, which is the case with Tanjiro to some extent as well, since he lost his entire family to demons, and earlier his father as well. “Tan” in the name “Tanjiro” is also written with a symbol for charcoal and his family is said to have worked with charcoal for a living, which is why the black sword makes sense once again aside from the orphaned loner trope.
Black in Japanese symbolism is also the color of protectors, and Tanjiro first entered the Demon Slayer Corp to protect Nezuko, his sister turned demon. Later on, we can see that Tanjiro is dedicated to protecting and saving complete strangers, often risking his own life and well-being to save others. Black swords in anime also have a role in out leveling unfair advantages, which aligns with the story of humans fighting super-powerful demons with Nichirin swords as their one of few ways of standing a chance against centuries-old human-killing machines that demons in Demon Slayer are.