Unlike Hyōdō, he is shown to be a tragic antagonist rather than a purely evil antagonist.
He reveals to Kaiji that he detests the life he leads, and claims to not know true friendship or love, as everyone he meets kisses up to him due to the influence of his father. As a result, he thinks human beings are naturally detestable and likely to betray others, and additionally he finds no issue in wasting money for his gambles and schemes, and instead wants to be an author.
As a means of finding out if true bonds actually exist, Kazuya sets up a series of deadly games designed to test the bonds between people, which influence the ideas for his novels. In addition, he runs a company called "Kazuya Corporation", which deals in covering up murders under the guise of suicides or construction accidents. Much like his father, he also has tendency to abuse his employees.
Despite his sadistic and arrogance attitude, he is in fact miserable due to his envy for his older brother Kazuki, as he is always being cast aside and ignored by his father and almost everyone in the company. This result in his addiction to gambling to prove his worth and vent his frustration.
Tobaku Datenroku Kaiji
Kaiji first encounters him at the casino Takashi Muraoka was running. Initially, he did not recognize him as the son of Hyōdō as Muraoka only referred to him as "young master".
After Kaiji loses all of his money during Mine Field Game “17 Steps”, he keeps loaning Kaiji money so Kaiji can continue to gamble; however, he tells Kaiji that if he cannot repay the debt then he will either be sent back to the underground labor camp or will have a random body part removed (which body part will be removed is determined by a lottery wheel). He also reveals that in the worst case Kaiji will have to be tortured and killed like 30 people ranging from 15 to 60 years old who lost their gamble with Kazuya.
Tobaku Datenroku Kaiji: Kazuya-hen
After Kaijis gamble, he offers him an opportunity to gamble with him. In his limo, he brings Kaiji to a graveyard to show him Kaijis grave in case he loses to him and makes him sign a contract on how his body will be managed. After signing the contract they relocate to a restaurant. Here he discusses human nature and shows Kaiji a gamble he created to the test of the bounds of friendship between three participants, the Salvation game.
After the conclusion of the Salvation game, he and Kaiji relocate to a warehouse where they do their gamble, One Poker. Before that, Kaiji insists to bring Chang and Mario with him to act as his support during the gamble in which Kazuya begrudgingly accepts.
Tobaku Datenroku Kaiji: One Poker-hen
After Kaiji defeats him in One Poker, he falls from a great height of the building as the condition of the loser but Kaiji, Chang and Mario manage to save him from the fall as an act of mercy. He is shown to be unconscious after they leave him to escape with the money he bet. Enraged with his son's condition and the loss of 2.4 billions Yen, Kazutaka commands the blacksuits and Endo to capture Kaiji, Chang and Mario to get the money back.
- Kazuya is the only antagonist so far in the series who Kaiji was willing to save from death as well as making Kaiji feel some level of sympathy towards.
- Kazuya is the only antagonist who has been closest to death in the series.