Demon Slayer has become wildly popular since its debut in 2020, following the story of a dedicated brother's journey to return his sister to her human form. Fans around the globe have been drawn in by the siblings and their unwavering allegiance to one another, as well as the quirky and well-built side characters who join them along the way.

Nezuko Kamado, younger sister to series protagonist Tanjiro, was introduced in her human form. As a human, Nezuko was kind, caring and maternal toward her younger siblings. After being transformed into a demon, it wasn't just her personality that changed -- her hair has as well.

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Flame-Colored Streaks Have Appeared in Nezuko's Hair

At the start of Demon Slayer, Nezuko lost both her family and her humanity in a tragic massacre at the hands of Muzan Kibutsuji, Lord of the Demons. Tanjiro and Nezuko were the lone survivors of the Kamado family, however, Nezuko was only able to survive because Muzan transformed her into a demon. This meant she developed a demon's craving for human blood -- and initially attacked Tanjiro.

With time, Nezuko learned how to withhold her human cravings and now regains strength through sleeping instead. However, the evidence of Nezuko's demon side is ever-present in her appearance. As a human, Nezuko had long, wavy jet-black hair, but since being transformed into a demon, vibrant fiery streaks have appeared. These streaks started small -- just a couple of colorful tips -- and were a nearly unnoticeable change.

However, as Nezuko began to spend time in demon form and use her powers more frequently, the flame-colored streaks appeared to grow and have become far more visual. For example, when Nezuko transforms into her advanced demon form in the "Entertainment District" arc, the changes in her hair color are most prominent and far more eye-catching.

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What Nezuko's Changing Hair Could Mean For the Future in Demon Slayer

Nezuko in her new form in Demon Slayer.

Demon Slayer often emphasizes how external forces affect the physical appearance of its characters. Zenitsu Agatsuma has bright yellow hair caused by a lightning strike, the Rengoku Clan has red and orange hair induced by their ancestors' diet, and the Kamado clan are Children of Fire, hence Tanjiro's reddish hair color. Along with this, demons having vibrantly colored hair is a common phenomenon within Demon Slayer, such as the spider demon Rui's white hair, or upper moon demon Gyutaro's green curls.

It's most likely that Nezuko's flame-colored hair is a physical sign of her demon side, a reminder to the audience that she's no longer the innocent girl from the village. The particular color of her hair would also be reminiscent of her family's history as Children of Fire, explaining the burnt red tinge at the ends of her hair.

This implies that Nezuko's hair color represents the demon blood within her; as the color takes over her hair, she may succumb to her demon side more often. Whether this is merely a theory can only be revealed in future episodes of the anime, but it's undeniable that Nezuko has lost control of her demon abilities in recent arcs. Luckily Tanjiro is always there to restore her humanity, but if Nezuko embraces her demon side much more, this may not remain a possibility.