The alteration of Nezuko’s hair is a result of her becoming a demon, a change that is similar to the demon, Rui, who appeared in the Mount Natagumo Arc as the main antagonist. Her transformation into a demon symbolizes the change in her hair color to black with vibrant orange tips, visually differentiating her from her former human self.
Additionally, her eyes became slit, further emphasizing her new demon nature. This physical change is consistent with other demons in the series, who all possess distinctive physical characteristics, such as fangs and skin color, that reflect their new identity.
A prevalent theory among fans is that the orange tips in Nezuko’s hair are a sign of her being one of the “Children of the Sun.” This theory is based on her relationship with her father, Tanjuro Kamado, who possesses knowledge of the powerful technique known as the “Dance of the Fire God.

What Changed in Nezuko’s Appearance?
When Nezuko was first introduced in Demon Slayer: Kimetsu no Yaiba season 1, episode 1, she had black hair, which she usually styled in a bun. However, as the series progressed, her hair color changed to black with fiery orange tips, which she now wears down.
Additionally, her eyes underwent a change, going from having red with a hint of pink and circular iris to becoming a bright pink color. Finally, she now possesses demon fangs and sharp claws. The change in Nezuko’s appearance serves to reflect the change in her nature and character.
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What Does Nezuko’s Pure Demon Form Look Like?
During Nezuko’s fight with Daki in the Entertainment District Arc, her pure demon form is depicted with several distinct physical features. Her body undergoes significant changes, becoming larger, taller, and more curvaceous, with her hair also growing longer. There are also vein-like patterns present on her face and other parts of her body.
One of the most notable additions is a short white horn on the right side of her forehead, which is decorated with an irregular crack pattern. Another striking feature of her demon form is the red and green vine-like pattern that covers her skin, circling around her arms, legs, and chest.
Read more: Do Nezuko and Zenitsu End up Together In Demon Slayer?