TV-Series
Description
Dayon is a recurring character who originally appeared in the Osomatsu-kun manga and anime before also appearing in the later spinoff series, Mr. Osomatsu. The character was created by Kenichiro Takai, an assistant to the original manga creator Fujio Akatsuka, who requested new characters to help expand the supporting cast. Dayon's name comes directly from his most distinctive trait, a verbal tic where he ends his sentences with the sounds dayon or simply yon.

Physically, Dayon is defined by his highly exaggerated and unusual features. He is a slender man with a large, exaggerated mouth that stretches his face to unrealistic proportions, typically showing a few prominent teeth. His head shape is unique, starting narrow at the top and widening considerably to emphasize his large mouth and jaw. He has a long, curly mustache and stubble covering his face. His hair is neatly slicked and parted to the sides. Dayon is almost always seen with a broad, open smile. His standard outfit is a khaki-colored suit with modern leather dress shoes, though earlier incarnations of the character in the original manga and 1960s anime depicted him wearing traditional geta sandals.

The character's personality is deliberately ambiguous and versatile, officially described by Fujio Pro as an unclear man whose true identity cannot be easily understood. He is often portrayed as a simple, easy-going individual, but his exact traits shift depending on the needs of the story. In the original Osomatsu-kun, Dayon functioned as a very adaptable bit character, frequently appearing in minor supporting roles such as a policeman, a shopkeeper, or any other part that a scene might require. In the later Mr. Osomatsu series, his role evolved into something more cryptic and surreal, often appearing as a phantom-like figure who simply smiles, observes, and performs strange, unexplained actions without any clear motivation. His large mouth is a frequent source of visual gags, primarily centered on his gluttony, as he can use it to swallow nearly anything, including food, garbage, and even other people.

Dayon's role in the story is that of a supporting background character who facilitates bizarre or humorous situations rather than driving the main narrative. He does not have a consistent personal history or development across the series. One of the more notable and surreal expansions of his character occurs in Mr. Osomatsu, where an episode reveals the existence of the Dayon Tribe. Inside his body is an entire civilization of beings that look like him, and it is shown that if a person remains inside him for too long, they will gradually transform into a Dayon-like being themselves. His relationships with other characters are not clearly defined and tend to vary. He is sometimes depicted as a friend of the eccentric scientist Dekapan, and in some iterations of the franchise, he has been shown to have a wife who shares his exact facial features, minus the mustache.

Beyond his distinctive appearance and verbal tic, Dayon's primary notable ability is the seemingly limitless capacity of his mouth. This is used both for comedic consumption and as a plot device to transport characters to the strange world inside him. His character has remained largely static, without any significant personal growth or backstory, serving instead as a consistently odd and unpredictable element within the chaotic world of the series.