Devil

Devil appeared before Kazuya Mishima, when he was thrown off a cliff by his father when he was a child. Devil proposed a deal to Kazuya. He would give him power to defeat Heihachi in exchange for his soul. Kazuya took the offer. Devil did corrupt Kazuya, bus was unable to fully take over his soul. Inside Kazuya, Devil and Angel fought each other for Kazuya's soul.

Jun Kazama tried to defeat the Devil inside Kazuya, but was able only to weaken him. During his weakened state Kazuya was defeated by Heihachi and was thrown into a volcano. The Devil left Kazuya's body to take over the body of his unborn son inside Jun. Jun was able to defeat the Devil, but a part of him went into the child.

The Devil returned into Kazuya's body and years later, after Kazuya was revived by the G Corporation, tried to make himself whole again by defeating Jin Kazama during the fourth King Of Iron Fist Tournament, with the help of Kazuya. But when he wanted to extract the Devil Gene from Jin something went wrong and now Kazuya has full control over Devil. They have become one entity.