In the world of Demon Slayer, where hashiras wield swords infused ... is as wild and tough as the mountains that raised him and his boar’s head mask is as much a part of him as his dual serrated ...

Since, Hinokami Kagura and Sun Breathing are the same, dancing all night might lead to the awakening of the demon slayer mark. The mask could be hiding an awakened mark. Muzan himself has shown ...