Nagisa Tezuka is identified as Shinobu Tezuka's older sister, with some sources alternatively listing her as his older cousin. She hails from a prominent political family marked by intense pressure and fierce sibling competition. This environment, where her parents favored Shinobu's achievements and neglected her, fostered Nagisa's deep resentment and feelings of inadequacy. It ignited a consuming, one-sided rivalry, driving her obsession with humiliating and undermining Shinobu through extreme measures.

Her actions include orchestrating the kidnapping of Shinobu's closest friend, Mitsuru Ikeda. Nagisa confined Mitsuru, employing psychological manipulation and forced disrobation to pressure Shinobu into submission. Her plan failed when Mitsuru deliberately injured himself to prevent Shinobu's capitulation, revealing his rapid facial healing. Kazuya Hasukawa's violent intervention then overpowered Nagisa's henchmen. In another scheme, she mistakenly kidnapped Reina Kisaragi, Shun Kisaragi's younger brother, confusing him for a girl due to his appearance and highlighting her persistent errors in judgment.

Nagisa operates using anonymous henchmen designated only as "A," "B," "C," and "D." She frequently leverages her family's wealth and influence to bypass rules, embodying a "Screw the Rules, I Have Money" approach, though these efforts consistently backfire. While her later appearances show no significant redemption, repeated failures and the resilience of Shinobu's allies gradually diminished her disruptive impact. Her character stems from familial neglect and unchecked resentment, maintaining a persistent antagonistic role.