Hailing from the Germ Planet, Baikinman arrived on Earth as an egg that hatched the same day Anpanman was born. He declares his sole existence is to defeat his destined rival, frequently proclaiming, "I was born to defeat you, Anpanman!" His appearance is that of an anthropomorphic fly: a black furry body, light pink eyes, purple lips, fly-like wings, a zigzag tail, and a slimy blue tongue. A distinctive purple dot on his chest functions as a microphone amplifying his voice. Exposure to soap or cleaning agents triggers a severe allergy, stripping away his mold-like coating and shrinking him to fly size or bleaching his body white. Yet defeats never deter him; he consistently recovers and returns.

A self-proclaimed genius scientist, he frequently invents complex machines, robots, and vehicles—often modeled after his face or color scheme—to execute elaborate schemes against Anpanman. His primary tactics involve spreading germs, stealing food driven by gluttony, and deploying minions like Dokin-chan, Horrorman, and Kabirunrun. He operates from a base shaped like his own head, reflecting his narcissism, and habitually uses the pompous self-referential pronoun "ore-sama." Though typically rude, loud, and impulsive, he occasionally reveals unexpected depth, like reluctantly aiding Anpanman during true crises or showing a soft spot for creations such as Franken Robo-kun, whom he treats as a son despite initial annoyance at the robot's affectionate electrocuting hugs. Creator Takashi Yanase suggested Baikinman harbors an underlying desire for a normal life, constrained by his inherent villain role.

His relationships are complex: he harbors unrequited feelings for his partner-in-crime Dokin-chan, who often bosses him around but remains his closest ally. He implanted Baikin Grass in Rollpanna during her creation to enforce her evil alignment, though she frequently rebels. Beyond the main series, Baikinman appears in spin-offs like "Mystify World: Mega Force" as part of Dr. Eggman's League of Villains and in video games such as "Paropuzzle Bobble." Recent films like "Baikinman and Lulun of the Picture Book" and "Chapon no Hero!" depict him adopting temporary heroic roles—revealing a character's secret origins or assisting allies—hinting at nuanced development beyond pure antagonism. His design inspired germ personifications in other media, including a banned Pokémon episode, and parodies like Vaccine Man in "One Punch Man," who shares his voice actor.