Head Demon is the first Demon encountered by Kamado Tanjirou.
The Demon had already been attacking travelers who take shelter at a small temple hut on the pathway that leads to the Narrow Mist Mountain. When Tanjirou was asking for directions, one of the villagers mentioned that it would be dangerous for him to travel at night as people had been going missing in the area.
When Tanjirou and Nezuko arrived at the hut, the Demon had just killed three people. When the Demon tried to strangle Tanjirou, Nezuko kicked its head clean off its body.
Even without a head, the Demon could still command its body to attack the siblings. The Demon also grew a pair of hands from his head. As the body was furiously attacking Nezuko, Tanjirou tackled the body and threw it off a cliff. However, this did not result in the Demon's death, although losing its body caused it excruciating pain.
Tanjirou had also pinned the Demon's head to a tree with his axe to stop its movements. As he was too compassionate, he failed to kill the Demon before dawn, accidentally allowing the Demon to perish by the sun's first rays instead.
After the Demon's death, Urokodaki Sakonji gave the Demon's victims a proper burial.
Head Demon is the first character in the manga that commented on Tanjirou's extremely hard head.
Some Japanese fans also call him "Temple Demon" or "Geodude".