Naoya
About
VA: Hiroshi Kamiya (Drama CD), Kishio Tanigawa (Overclocked), Kyle Hebert (English)
Kazuya's cousin, who lived with him until a few years before the story. He wrote the Demon Summoning Program.
It is revealed that he is the reincarnation of Cain. As punishment for murdering Abel (part of whom's reincarnation lies within the protagonist), God punishes Cain by forcing him to remember his sin for all of eternity, carrying the memories of the murder throughout all future lives. As a result, Cain's resentment towards God grew. Once the protagonist became eligible for becoming the King of Bel, Naoya tried to persuade the protagonist to use that power to overthrow God.
(Source: Wikipedia)