Kaiji Soze is a Japanese voice actor and stage actor associated with the Theater Studio Live company. He was born on October 18th in Sendai, Miyagi Prefecture, and has O-type blood. Soze's path to performance began after graduating from Waseda University and working at a record company that dissolved after two years. He then pursued his aspiration to become an actor, joining the Theater Studio Live troupe in 1996 as a second-term student. His stage name is a play on the character Keyser Söze from the film The Usual Suspects. He originally performed under the name Kaiji Soze using different characters before changing to his current written form in the autumn of 2007.

Soze's career is notable for its integration of voice acting with motion capture performance. He made his motion actor debut in the 2013 CGI animated film Space Pirate Captain Harlock, and it is common for him to perform both the voice and motion capture for a single character in a project. His role in the Ultraman anime series exemplifies this dual skill. He voices the character Bemular across multiple seasons of the show, a role he has played since the first season in 2019. For Ultraman, Soze also served as the motion capture actor for both Bemular and the character Mitsuhiro Ide.

Soze has a recurring professional relationship with directors Kenji Kamiyama and Shinji Aramaki. He has been a cast member in their CGI anime productions, including the Ultraman series and the Ghost in the Shell: SAC2045 franchise. In Ghost in the Shell: SAC2045, which began in 2020, he provides the voice for the character John Smith, a role he has continued in subsequent films and seasons associated with the series. His other notable anime credits include the role of Fujiwara no Tadanobu in the 2012 historical romance series Chōyaku Hyakunin Isshu: Uta Koi and the role of Yukio Kurobe in the same year's Shin Tennis no Ōjisama. Among the industry professionals he has worked with on multiple occasions are voice actors Megumi Han and Kenjiro Tsuda, as well as directors Aramaki and Kamiyama.