The main protagonist and a Limiter who enrolls at West Genetics. His sister, Kazuha Aoi, sacrificed her life to defeat a powerful Nova who invaded Japan in the past and after empathizing with Satellizer, whom he believes resembles his sister, he decides to become her limiter. Despite being male, Kazuya can nurture stigmas in his body and due to his exceptionally high synchronization rate with those stigmas, he can use his freezing ability without having to perform the ceremony that would allow him to unify his senses with a specific Pandora, otherwise known as being "baptized". In addition, his freezing can completely immobilize anyone he uses it on and can also break the freezing abilities of multiple Limiters. This makes him a perfect partner for Satellizer since she refuses to be baptized with a Limiter, seeing it as some form of lewd act.