Zero, also known as Pukko in the original Japanese version, serves as a lieutenant in the Galactic Patrol's 4th squad. His mission involves assessing humanity's violent tendencies to determine if Earth warrants destruction by an anti-proton bomb. To observe humans undetected, he adopts a duck disguise upon arrival.

Zero exhibits a cynical and short-tempered nature, frequently expressing disdain for humanity and initially advocating strongly for Earth's annihilation. He often clashes with his more empathetic team leader, Bokko, especially regarding their young human ally, Shinichi. Despite this gruff exterior, Zero possesses technical expertise as an engineer, designing blueprints built by teammate Nokko. He also demonstrates an unexpected appreciation for Earth's culture through his recurring skill as a guitarist.

Throughout events, Zero's rigid stance subtly shifts. While remaining the most vocal proponent of destruction, his loyalty to the team and protective instincts toward Shinichi surface during critical moments. This internal conflict peaks when the Galactic Federation orders Earth's destruction. Witnessing Bokko's defiance and Shinichi's plea for humanity's redemption, Zero experiences profound regret for his earlier harsh judgments. Following the council's decision to delay judgment, he openly expresses shame for his prior attitude, acknowledging a newfound understanding of humanity's potential for growth.

His development concludes with a symbolic act of solidarity: joining Nokko to transform Bokko into a human form, enabling Bokko to stay with Shinichi, signaling Zero's acceptance of the deeper emotional bonds formed on Earth.