Shiro Mizuki is a character from the movie 'Kamen Rider Agito: Project G4', which is part of the Kamen Rider Agito series. He is the pilot of the experimental Kamen Rider G4 system, a government-developed rider suit designed for military use. Driven by a sense of duty and ambition, Mizuki becomes the primary antagonist in the film, clashing with the main Riders. His role highlights the dangers of weaponizing Rider technology and the ethical dilemmas faced by those who wield such power.