Nami Kozono, the wealthy student council president, arrives daily in a chauffeured white limousine and commands several thugs. She sports distinctive violet hair in a high ponytail secured with a pink bow, and amber eyes. She wears the standard academy uniform to school, but favors elaborate outfits outside, like a red jacket with a fur collar over a purple top, gold earrings, a crucifix necklace, and dark boots. For occult rituals, she dons a black robe.

Openly lesbian, Kozono maintains a dominant relationship with fellow council member Junko Mochida, often engaging sexually at school. She later develops an obsessive crush on transfer student Reika Kitami, repeatedly attempting seduction despite rejections; one attempt during tutoring involves groping Kitami, resulting in a physical rebuke. Arrogant, cruel, and entitled due to her status, Kozono coldly dismisses others, like rejecting male student Hiratani's advances by stating her disinterest in men and his unworthiness.

Her introduction to the occult occurs when she interrupts Hiroko Takashiro's tarot session, ridiculing their interests and blocking their witchcraft club request. After witnessing Takashiro's group use a Bible Black spell to force Mochida to publicly masturbate during assembly, Kozono grows suspicious. Soon after, Takashiro's group, at Hiratani's request, magically compels Kozono into an obsessive, submissive love for him. Under this curse, she neglects duties and engages in repeated sex acts with Hiratani.

Freed from the love spell by Takashiro, Kozono reacts with disgust and rage, directing her thugs to brutally beat Hiratani. She then renews her pursuit of Kitami, pleading for "purification" through sex, only to be slapped and rejected again. Seeking power and revenge, Kozono joins Takashiro's Rose Cross witchcraft club. During a demon-summoning ritual that results in Takashiro's violent rape and hospitalization, Kozono observes with awe. Exploiting Takashiro's absence, she seizes control of the club and pushes forward with a plan to summon the Devil on Walpurgis Night, dismissing warnings about the risks.

For the ritual, Kozono orchestrates Kitami's kidnapping, permitting her thugs to rape her non-vaginally to preserve her virginity for the sacrifice—a condition ignored by one thug, unbeknownst to Kozono. When Takashiro attempts to halt the ritual, Kozono uses a rudimentary spell to repel her and orders her confinement. During the ceremony, Kozono stabs Kitami with a black sword as a sacrifice. The ritual fails due to Kitami's lost virginity, causing panic among the club members. Kozono then murders them all with the sword, declaring they had "lost their sanity" by dabbling in magic. As the gates of hell begin to open, Kozono reaches out for the Devil's power but is stabbed multiple times in the back by a dying Kitami, leading to her death before achieving her goal.

In the original Bible Black game, Kozono appears briefly as the "Priest" presiding over Kitami's sacrifice ritual, depicted with blond hair and red robes—a visual contrast to her anime depiction. Like the anime, she murders her fellow club members after the ritual fails and is killed by Kitami. Her role remains consistent as an ambitious antagonist whose pursuit of power culminates in violence and her downfall.