Dayon originated as a character in the original *Osomatsu-kun* manga and anime, created by Kenichiro Takai at Fujio Akatsuka's request to expand the supporting cast. His name stems from his verbal tic of ending sentences with "dayōn" or "yon".

Physically, Dayon possesses an exaggeratedly large mouth, stretching his face into unrealistic proportions. He typically appears slender, wearing a khaki-colored suit with neatly slicked hair parted to the sides. His head shape narrows at the top and widens toward the mouth, accentuating this feature. Facial stubble and a long, curly mustache are consistent traits. His footwear varies: early depictions show geta sandals, while later iterations feature modern leather dress shoes.

His personality is deliberately ambiguous and versatile. He often appears easygoing but adapts to various minor roles. A recurring gag exploits his mouth's capacity for gluttony, capable of swallowing objects like food, garbage, or even people. This trait facilitates surreal humor, such as in the *Osomatsu-san* episode "Dayon Tribe," where characters become trapped inside his body. He also demonstrates unexpected interests, like composing haiku in early *Osomatsu-kun* appearances.

In *Osomatsu-kun*, Dayon functioned as a flexible background character, frequently cast in utilitarian roles like a policeman or shopkeeper, his design allowing him to fill any minor part needed.

In *Osomatsu-san* and related media, Dayon's role shifts toward the cryptic and absurd. He often materializes as a silent, smiling "phantom" performing unexplained strange actions. In "Dayon Tribe," he inhales the Matsuno brothers after a drunken stupor, transporting them to a surreal internal world inhabited by identical Dayon beings. Here, Choromatsu nearly marries a female Dayon after assimilation, highlighting escapism from societal pressures. The theatrical film *Osomatsu-san: The Movie* includes Dayon as a background presence, shown drunk on the streets and attending a high school reunion. A past version appears in the "world of memories" segment, where an interaction with the adult sextuplets causes his head to explode and reshape comically.

Across all media, Dayon remains a peripheral figure lacking significant development or backstory. His primary narrative function is facilitating bizarre or humorous situations through his physical traits and enigmatic demeanor.