Kazuaki Hirata leads the Shinseikai yakuza group, having previously served as its second-in-command. He assumed leadership when Takahito Misumi stepped down, with Misumi mandating Yashiro as Kazuaki's new second-in-command to formalize the transfer of power, thereby cementing Kazuaki's authority.

Physically, Kazuaki has short dark hair. In the anime adaptation, he wears an unbuttoned green suit jacket over a purple collared shirt. His design adheres to classic yakuza aesthetics, frequently featuring him smoking.

Kazuaki shares a significant history with former leader Takahito Misumi, who described their bond as initially romantic before evolving into a brotherly dynamic. Kazuaki maintains a professionally distant relationship with his second-in-command Yashiro, pragmatically acknowledging Yashiro's financial management skills and noting his pronounced sexual appetite, though their interactions lack trust or warmth.

Within the narrative, Kazuaki advances plotlines tied to organizational conflicts and financial operations, exemplified when he cites money-making activities during discussions with Yashiro, highlighting his focus on the group's economic interests. His background includes overseeing Shinseikai's operations after Misumi's departure.

The etymology of his name combines "harmony, peace" and "bright" for Kazuaki, while Hirata signifies "flat, broad, level, even, peaceful" and "field, rice paddy".