The Tongue Demon took the form of a muscular man with gray skin and very dark blue hair, set noticeably far back on his head to make room for the two small horns that protruded from either side of his forehead. He had two pairs of eyes, one large and cat-like of a green color and the other more squinted and set above the first, their irises red. His most notable features were his extremely long tongue and the navy blue arrows that patterned his nose and forearms, a large blotch of a similar color on each temple.
The Tongue Demon wore nothing above his waist, under which he sported only the bottom half of a patterned knee-length yukata.
The Tongue Demon, as with many others of his kind, was a ruthless being who seemed only to care about eating any and all humans that crossed his path. He appeared to be somewhat unintelligent, as he often talked to himself and repeated words when speaking as well as slithered around on the floor rather than walking.
The demon's past is unknown. However, he lived in the same house with the Horned Demon and Kyogai. They often fought for the victim.
Just as Zenitsu tells Shoichi to refrain from making any loud noises to avoid attracting any demons, he shows up in behind the duo, further terrifying an already trembling Zenitsu, additionally passing a remark about how good eating a child might feel on his tongue.
Starting to sprint away, Zenitsu desperately tells the demon to stay back, additionally saying that saying neither he nor Shoichi would taste good as they begin to run away. The Demon simply responds by saying that he would not know how they'd taste if he didn't try, proceeding to chase and attack them; slicing through a vase with ease.
Just as he enters the room, an unexpected gesture occurs as the his tongue gets cut off by Zenitsu as the latter stands with his head hung low; subconscious sustaining him. Moving into the stance for using Thunder Breathing, First Form: Thunderclap and Flash, Zenitsu gets ready to decapitate the tongue Demon without hesitation. With one swift move and a direct slice from the Zenitsu's Nichirin Sword, the Demon's head now lies on the ground, as Zenitsu easily goes through with his plans; now standing victorious against the demon in battle.
As Zenitsu wakes up; control from subconscious fading away, he screams at the sight of the Demon's decapitated head.
Flesh Manipulation: This demon has displayed the ability to manipulate the length, speed and sharpness of his tongue, being able to slice a vase with ease.
- Kimetsu no Yaiba Manga: Chapter 22 (Pages 18-19).