Emerging from the "Germ World" as an egg hatching simultaneously with Anpanman's birth, Baikinman stands as the primary antagonist, embodying moral dualism opposite Anpanman. His anthropomorphic germ form resembles a fly, featuring a black furry body, fly wings, a zigzag tail, purple lips, a slimy blue tongue, light pink eyes, and large teeth. This design draws inspiration from Beelzebub, the demonic "Lord of the Flies," and specifically embodies black bread mold (*Rhizopus stolonifer*), positioning him as Anpanman's thematic enemy.

Narcissistic and impulsive, Baikinman relentlessly obsesses over defeating Anpanman, his self-proclaimed destined rival. He frequently engages in theft, bullying, and elaborate schemes involving mechanical creations to spread germs or sabotage Anpanman, driven by gluttony and his identity as "a being who knows no love." Creator Takashi Yanase indicated Baikinman harbors an underlying desire for a normal life, constrained by his inherent antagonistic role. His relationships reflect complexity: primarily adversarial toward Anpanman, he occasionally cooperates reluctantly against greater threats, sharing moments of non-conflict outside main storylines. He exhibits unrequited affection for Dokin-chan, enduring her bossiness and affection for Shokupanman, and displays a paternal soft spot for Franken Robo-kun, a robot he created who inadvertently electrocutes him during attempted hugs. He engineered Rollpanna's blue "evil heart" by implanting a Baikin Plant during her creation, though she often defies his control.

A critical weakness is his severe allergy to cleanliness: exposure to soap or water causes dramatic shrinking or his entire body turning white, drastically reducing his threat capability. In media beyond the core series, such as the movie *Kuroyukihime to motemote Baikinman*, Princess Kuroyukihime manipulates him, admiring him and coercing him into spreading darkness until Anpanman and Dokin-chan intervene. His thematic role extends beyond mere villainy; Yanase's wartime starvation experiences informed Baikinman's embodiment of insatiable greed, contrasting Anpanman's symbolism of sustenance and compassion.

Character development reveals nuanced dimensions: newer episodes depict increased tolerance toward Franken Robo-kun, and his occasional alliances with heroes suggest situational flexibility, though his core drive to antagonize Anpanman remains unchanged.