Tanjiro, a young Demon Slayer with his nichirin sword, travels from place to place killing demons and protecting humans. His sister, Nezuko, is always traveling with him, in a box during the day to hide from the sunlight and outside underneath the moonlight when nighttime. Tanjiro doesn't have a current mission, so he took a break to enjoy the inn of the town he recently liberated of a demon, enjoying the local udon and the lantern lights of their celebration.

But then, Tanjiro smells something odd. He quickly finishes his udon and pays the good food vendor, then follows his skilled nose.