Kazuki Nakashima was born on August 19, 1959, in Fukuoka Prefecture, Japan. Before establishing himself as a prominent anime screenwriter, his career began in theater. He joined the renowned theater company Gekidan Shinkansen as a resident playwright in 1985, a role through which he developed a signature style of high-energy, action-driven historical romances. His stage work, which includes acclaimed productions such as Aterui and Seven Souls in the Skull Castle, has earned him prestigious honors including the Kishida Kunio Drama Award and the Matsuyo Akimoto Prize.

Nakashima is widely recognized for his prolific output as a screenwriter and series composer in anime. He has often collaborated with director Hiroyuki Imaishi, a partnership that began with the 2007 mecha series Gurren Lagann, for which Nakashima served as series composer and scriptwriter. This collaboration continued at Studio Trigger, where he wrote the original screenplay for the 2013 action series Kill la Kill and co-wrote the 2019 theatrical film Promare. His other notable anime credits include serving as the original creator and head writer for BNA: Brand New Animal (2020) and the series Back Arrow (2021). His work extends to film adaptations of existing properties, such as the screenplay for Batman Ninja (2018).

Beyond animation, Nakashima has made significant contributions to the tokusatsu genre, notably as the main screenwriter for the television series Kamen Rider Fourze (2011). His background as an editor for the publisher Futabasha also informed his work; he was a noted fan and editor of manga artist Ken Ishikawa, whose series Getter Robo served as a major influence on the themes and energy of Gurren Lagann.

Nakashima's artistic identity is characterized by a blend of over-the-top action, dramatic spectacle, and narratives that prioritize passionate, heroic determination. His writing frequently draws on his deep appreciation for manga, kabuki theater, and tokusatsu, resulting in a style that combines historical and mythological motifs with modern, exaggerated, and energetic storytelling. This unique fusion has made him a significant figure in contemporary anime, directly shaping the stylistic identity of Studio Trigger and leaving a lasting impact on the mecha and action genres.