The Swamp Demon was a Demon that went on a rash of kidnappings during Kamado Tanjiro's first mission for the Demon Killing Corps.

The Swamp Demon was a pale skin young man with long blue hair with two long strands of violet on both sides of the face, supported by two golden hair separators. As usual in several demons, he had claw-like nails and the veins on his forehead are quite prominent, in his case, to the point of replacing his eyebrows. His eyes were red without pupils and with prominent dark eye bags. Because he could be divided into two demons apart from himself, each demon differed from the other in the number of horns and clothing. The three demons wore shinobi clothing.

The main body had a single horn in the upper center of its forehead and wore a full-length long-sleeved shinobi uniform with meshes on its wrists and neck, the mesh of the neck having three small ribbons centered hanging from it. There were divisions inside his uniform coat where he could keep the collection of hairpins of his victims.

The second body had two horns, one on each side of its forehead. His shinobi attire did not have sleeves, instead, it had two small triangular meshes in the armpit area and a large triangular mesh in the chest area.

The third body had three horns, each in the position in which the other two bodies had their own horns and wore a shinobi garment sewn with meshes on both sides of the arms, shoulders, and thorax. Under his coat, he wore a sleeveless bottleneck shirt.

(Source: Kimetsu no Yaiba Fandom)