Kazunari Ninomiya, born June 17, 1983, in Tokyo, is a Japanese entertainer whose career encompasses singing, acting, and voice acting. He began his entertainment career in 1996 at the age of 13 when he joined the Johnny & Associates talent agency. Prior to his debut as a singer with the boy band Arashi in 1999, he started his acting career in stage productions. While he is widely known for his extensive work in television drama and film, his voice acting roles, though fewer in number, are notable performances in major animated projects.

Ninomiya's first experience with voice acting came in 2006 when he was cast in the lead role of Kuro in the animated film Tekkonkinkreet. In this film, he voiced the character Kuro, also known as Itachi, one of two orphaned street kids who protect their home in a surreal cityscape. This role marked his entry into the field of anime voice acting.

He returned to voice acting nearly a decade later for a high-profile role in the live-action and animated film adaptations of the popular manga Assassination Classroom. In the 2015 live-action film Assassination Classroom, Ninomiya provided the voice for the CGI character Koro-sensei, the titular creature who serves as a homeroom teacher to a class of students tasked with killing him. He reprised this voice role for the 2016 sequel, Assassination Classroom: Graduation. His contribution to these films was part of a larger commitment to the project, as he was the voice of the character in both installments.

In addition to his roles in Tekkonkinkreet and the Assassination Classroom films, Ninomiya also took on a voice role in the 2022 live-action film Tang and Me, where he voiced the character Tang, a robot.

Ninomiya's work as a voice actor, while a smaller part of his overall career, has been part of projects that achieved both commercial success and critical recognition. His performance as Kuro in Tekkonkinkreet is a noted part of his filmography, and the film itself is considered a visually distinctive and compelling animated work. The Assassination Classroom films were commercially successful in Japan. His achievements in acting overall have been recognized with numerous awards, including multiple Japan Academy Prizes and a Galaxy Award for his work in television dramas.