Iyami recurs across franchise iterations, originating in Fujio Akatsuka's "Osomatsu-kun" manga. He first appeared as a background character in a 1963 chapter, evolving into a defined persona named and depicted as a nuisance to the Matsuno family by the next chapter. Physically, he possesses a tall, slender frame, a large protruding overbite showing three prominent teeth, a thin black mustache, narrow eyes, and a smooth bob hairstyle typically colored black or deep brown. He frequently wears a tattered pinkish-purple suit with loose socks that comically spring out during his signature "sheeh!" expression. Some narratives reduce him to symbolic features like a floating hat and teeth, reflecting themes of invisibility. Iyami insists he is from France, often claiming to have "just returned" and using French phrases like "bonjour." Evidence suggests this is an affectation rooted in Francophilia. His speech includes quirks like referring to himself as "me" and others as "chimi," ending sentences with "zansu." His trademark "sheeh!" vocalization involves a pose with one arm raised, one leg springing up, and his sock loosening. His personality blends flashiness, childishness, and self-centeredness. He engages in scams, theft, and lies, primarily to fund a return to France or secure necessities, though his plans often fail. Despite opportunistic and unhygienic tendencies like eating from trash cans, he occasionally demonstrates kindness, such as secretly providing for Chibita. He fluctuates between vanity, cowardice, and emotional vulnerability, exhibiting intense joy, grief, or tantrums. Relationships define much of his role. He maintains a rivalry with the Matsuno sextuplets, particularly viewing Osomatsu as his nemesis. His dynamic with Chibita oscillates between partnership in schemes and genuine camaraderie, with Chibita being one of the few receiving his empathy. Familial ties include an unnamed brother mistaken for him, a mother referenced in a locket, and inconsistently depicted relationships with a wife and daughter—all sharing his dental trait. His narrative significance varies across media. He and Chibita were protagonists in the 1988 anime, while later adaptations like "Osomatsu-san" relegated him to supporting roles. Alternate timelines, like a 1993 advertisement story, depict him as an aging bartender with gray-streaked hair, suggesting eventual stability.