Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train explained the main weakness of Tanjiro Kamado's black sword! When Tanjiro Kamado first started his journey with the Demon Slaying Corps, he acquired a specially crafted blade. But when he grabbed onto it, it became a fully black sword that seemed to carry a strange stigma with it. It was implied that Tanjiro's black sword would become a hindrance to his fighting the demons (as it was implied that those with black swords don't live for long), but the new movie dug into the main weakness of this unique blade color.
Picking up shortly after the events of the first season, Tanjiro has boarded a mysterious train together with his sister Nezuko and Zenitsu Agatsuma and Inosuke Hashibira. The main difference for this mission from those of the first season, however, is that they are boarding the train to support the Flame Hashira Kyojuro Rengoku in his mission. It's here that Tanjiro learns some big clues about his Breathing techniques and sword.
Upon meeting the Flame Hashira for the first time, Tanjiro decides to use this opportunity to ask Rengoku about whether or not he knows about how Tanjiro's father adapted the Hinokami Kagura dance into a Flame Breathing technique. While Rengoku does not know, he does reveal the main weakness (and negative perception) of Tanjiro's black Nichirin Blade.
Rengoku mentions that those with a black blade don't really have a chance of becoming a Hashira (the strongest fighters who have mastered their respective Breathing elements) because they usually can't decide on an element to master. This is Tanjiro's case as well because while he has learned Water Breathing techniques, from Episode 19 and on, Tanjiro's been pulled toward Flame Breathing.
Rengoku notes that this is a weakness, but there is a loophole as well. Noting how each generation of Hashira usually has a swordsman who can use both Water and Flame Breathing techniques, this does open the door for Tanjiro to eventually grow into this position. Rengoku even gives Tanjiro a critical clue to this new elemental mastery in the film as well.
So while Tanjiro has an inherent weakness in his black blade, it could also become his greatest strength if Tanjiro can not only master Water but the Flame element as well. There's a precedent, so that also means there's a roadmap to follow should Tanjiro decide to pursue the Flame element more.
But what do you think? How did you feel about the Demon Slayer movie? Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train is now screening in theaters, and you can check out our full review of the film here. Let us know your thoughts in the comments or you can even reach out to me directly about all things animated and other cool stuff @Valdezology on Twitter!