Talk:Nichirin Sword/@comment-26064296-20190504185857/@comment-43485542-20190813015633

I think the nature of Tanjiro's blade is related to his family history, as pointed out its black like charcoal, the very material his family has made for centuries. Charcoal is highly efficient as a crude man made fuel goes, and it has been a common material for forging swords. And these two symbolisms are important to remember when Nezuko enters the picture.

Now, its noted Tanjiro's sword turns from pitch black, like inactive charcoal, to crimson red, like active charcoal, when Nezuko uses her Blood Burst on it. Now, not only does the color change but the sword becomes far stronger and makes Dance of the Fire God styles more effective (a special fire type breathing). So symbolically, the 'charcoal' sword is 'reforged' in fire.

In other words, we can interpret Tanjiro's sword is usually 'inactive' when its black, and when it turns crimson red its releasing its true strength, all akin to charcoal and when it burns. And his ancestor wielded a sword of the same nature no less.