Tatsuo appears in the "Beast City" OVA series as a high school student navigating a dystopian near-future Japan infested with deadly "Beasts." Despite the perilous environment where humans are hunted, he obsessively pursues romantic or sexual encounters with multiple female classmates, fixating on "anything in a skirt."

His childhood friend Megumi declares herself his girlfriend and exhibits extreme possessiveness, resorting to public acts like masturbation to capture his attention. Tatsuo consistently disregards Megumi, prioritizing other female classmates instead.

A later narrative revelation discloses that both Tatsuo and Megumi are non-human entities. Their true nature carries catastrophic genetic implications capable of ending the world, contextualizing Megumi's relentless fixation despite Tatsuo's rejections. This genetic connection and its apocalyptic potential form a core aspect of Tatsuo's background.

Initially, Tatsuo provides comedic relief through exaggerated romantic pursuits and absurd scenarios. His role shifts dramatically as the series adopts a darker tone, intertwining him with tragic developments. The story explores the consequences of his and Megumi's non-human existence amid escalating threats, including government-sanctioned nuclear annihilation, transforming Tatsuo from a comedic side character into a pivotal figure within the narrative's tragic, apocalyptic stakes.