Yes, Tanjiro’s sword does turn red during battle. This transformation occurs when Tanjiro is in a state of intense concentration and focus, and it is a result of his unique fighting style and special abilities.

In the anime and manga series “Demon Slayer: Kimetsu no Yaiba,” Tanjiro Kamado is the main protagonist and a demon slayer. He wields a special sword made from a rare ore called Sun Steel, which is capable of killing demons. However, the sword alone is not enough to defeat the powerful demons that Tanjiro faces in battle.
To enhance his sword’s killing power, Tanjiro developed a unique fighting style called the “Water Breathing” technique. This technique involves breathing and movement patterns that allow Tanjiro to channel his inner strength and focus it into his sword strikes. As he gains more experience and becomes stronger, his sword and attacks become more powerful.
The transformation of Tanjiro’s sword into a red color occurs when he reaches a state of intense concentration and focus called the “Total Concentration – Constant” technique. This technique is a high-level form of the Water Breathing technique that requires the user to maintain a constant and unwavering focus. By doing so, the user can increase their physical abilities and channel their strength into their attacks.
When Tanjiro activates the Total Concentration – Constant technique, his sword begins to emit a bright red color. This transformation is a sign that Tanjiro has reached a new level of power and focus, and his attacks become much stronger and more effective. The red color of his sword is also a symbol of his determination and willpower, as it represents the burning passion that fuels his fighting spirit.
It is worth noting that the transformation of Tanjiro’s sword into a red color is not permanent. It only occurs during moments of intense focus and concentration, and it fades away once he loses that state. However, Tanjiro can also maintain the red color of his sword for a brief period by using the “Hinokami Kagura” technique. This technique involves a dance-like movement that channels the power of the sun into Tanjiro’s attacks, allowing him to defeat even the strongest of demons.
In conclusion, Tanjiro’s sword does turn red during battle when he activates the Total Concentration – Constant technique. This transformation is a symbol of his intense focus and determination, and it enhances the killing power of his sword. While it is not a permanent transformation, it is a significant factor in Tanjiro’s fighting style and abilities.