Concept and creation
Kazuya Mishima was modeled after author Yukio Mishima
Tekken producer Katsuhiro Harada created Kazuya Mishima as a corrupted character with a "pure dark side" as opposed to his father Heihachi Mishima, who Harada identified as having a more "human dark side". The franchise's design team referred to Kazuya and Nina Williams as "the soul [or] the cool part" of the original 1994 game. Kazuya's design and characterization was influenced by a variety of sources. Kazuya's family name was taken author Yukio Mishima, who was also used a model for the character's physical appearance. Harada compared Kazuya to a yakuza, while artist Takayuki Yamaguchi based the character's Tekken 6 costume on a robot. When describing Kazuya's personality, Harada cited him, along with Heihachi and Jin Kazama, as the violent characters of Tekken; he described the family as too quarrelsome. Denying claims that Tekken's plot is too convoluted, Harada said that its basic story is a "simple" struggle among members of the Mishima family with other characters dragged into the conflict. Harada described Kazuya as focused on power; writing that the character addresses "different types of power", he explained: "that's kind of the story of Tekken and it's shown as the certain reality of people themselves rather than the idea law and order."
Namco created Tekken 7's storyline as a conclusion for Kazuya's struggle with Heihachi, though the company wanted the game's overall plot to be easily understood by newcomers. Harada also wanted the game to flesh out the characters' relationship and reveal why they are enemies. As part of the promotion for Tekken 7, he said that either Kazuya or Heihachi would die in their final fight. The game's story mode includes a young Kazuya during the time Heihachi threw his son through a cliff following a fight; Harada said that the version of the character may be playable depending on fan demand. Harada called Kazuya's final fight with Heihachi a "major milestone in the storyline". Surprised by the length of the rivalry between the characters and Tekken's popularity as a franchise, he felt it necessary to end in a fight to the death. Although Kazuya's rivalry with Heihachi ended in Tekken 7, his relationship with his son Jin was left unresolved. Harada said that Jin's mother Jun Kazama would be "an important and essential element in talking about the story of Kazuya and Jin".
Kazuya has appeared in games with Street Fighter characters. Kazuya fights Akuma during the end of Tekken 7's story mode; Harada explained that the outcome of the fight was intentionally ambiguous, saying: "It’s still a work in progress." He joked that a scene with either character winning or being killed could negatively affect Namco's relationship with Capcom, particularly Capcom CEO Kenzo Tsujimoto. Kazuya teamed up with Nina for the crossover game Street Fighter X Tekken. When creating the illustrations for the characters, artist Kazuma Teshigawara said that he wanted them to complement one another. Nina was selected for the game instead of Anna Williams since her cold personality was similar to Kazuya's. The two characters were featured in the game's first trailer in a fight against Street Fighter characters Ryu and Ken Masters; the trailer was intended to attract the audience with the game's main feature. Completing the game with Kazuya and Nina unlocks ending scene where Nina is revealed as an agent who escapes from Kazuya's forces. Artist Toshio Ohashi described the ending as the game's most cinematic due to similarities between the characters.
Devil persona and voice actors
Kazuya's devil persona was created to meet Bandai Namco's request for more unrealistic characters in Tekken, such as Kuma, in contrast with the Virtua Fighter fighting series. The Devil is unlockable as an alternate skin for Kazuya in the first game, though he appears as a separate character for Tekken 2 with similar moves to Kazuya. The Devil fights with a laser, Inferno (インフェルノ Inferuno), through his staff and a pair of wings were added later in the game's production. He was made more powerful, with his ten-hit combo easily taking down enemies. Realizing how powerful the character had become, Namco decided to balance his moves before the game's release. The devil form is said to be based on Go Nagai's manga Devilman, where main character Akira Fudo develops a similar appearance. Although Kazuya's devil persona had first appeared as a single character, in Tekken 4 he was removed from the cast; according to Harada, Kazuya (unlike Jin) embraced the powers of the devil. In homage to Tekken: Blood Vengeance, Kazuya's devil form from the film was added as an alternate version of the character for Tag Tournament 2.
From the first Tekken to Tag Tournament, Kazuya has been voiced by Jōji Nakata. For the film Tekken: Blood Vengeance, writer Dai Satō added Jin and Kazuya as "visual eye-candy" similar to the Williams sisters (Nina and Anna). Satō wanted the pairs to be played together in the spin-off game Tekken Tag Tournament 2, which relies on two-person teams. Japanese voice actor Masanori Shinohara enjoyed Kazuya's role in the Tekken CGI film, and hoped his fans would see him in action.