Chibi-Zero, known as Chibi Zeroro in his tadpole stage, is the juvenile form of the character later called Dororo. This light blue Keronian tadpole wears a yellow cap marked with a red shuriken symbol and a medical mask, also bearing a yellow shuriken marking on his stomach.

Zeroro possesses a timid nature, easily frightened and prone to tears under stress. Yet, he reveals underlying bravery when intervention or protecting others becomes necessary. His personality is significantly shaped by interactions within his friend group, particularly his complex dynamic with Keroro. While considering Keroro a friend, Zeroro endures frequent bullying from him, including forced participation in dangerous activities that contribute to later psychological trauma. This treatment leads Zeroro to label Keroro as "mean," though he remains loyal, often following Keroro's instructions and visibly cherishing rare affirmations of their friendship.

In contrast, Zeroro shares a more supportive bond with Giroro, who actively protects and comforts him during distress. Giroro refrains from joining Keroro's harassment, acting as either a defender or passive bystander for Zeroro. Zeroro also maintains a respectful friendship with Pururu, typically aligning with her views in group settings. Beyond the core group, he uniquely understands Joriri's cryptic communication, considers Kikaka a valued friend after being rescued by him from an Andromedian husky, and previously shared a close bond with Zoruru before drifting apart due to Zeroro's deepening ties to Keroro and Giroro.

A pivotal childhood event is the Kero Ball incident. Zeroro becomes accidentally trapped inside the device alongside Keroro, Giroro, and Pururu after Keroro activates it while attempting to impress Pururu. While navigating internal obstacles to escape, Zeroro experiences significant distress. This ordeal contributes to a series of traumatic childhood experiences ultimately influencing his development into a stealth-focused assassin as an adult. The incident exemplifies his role within the group, often suffering unintended consequences during Keroro's misadventures.

Zeroro's background includes a close familial bond, particularly with his mother, though specific details about his family life beyond this emphasis on maternal affection remain limited.