Devil Gene

In the Tekken video game series, the Devil Gene is a mysterious curse that befalls several individuals within the Mishima bloodline, including Jin Kazama.

Information
It is unknown who in the Mishima bloodline originally held the gene. The curse is first described when Kazuya Mishima was a child and was thrown into a deep ravine by Heihachi Mishima, who wanted to test his son's strength. Kazuya survived the fall but only after he sold his soul to Devil in order to exact revenge on his father. However, due to the introduction of Jinpachi Mishima in Tekken 5, and some of the dialogue found within the game's story mode, there is some evidence that the Devil Gene may predate this.

History of the Devil Curse/Gene
Prior to Tekken 4, the Devil was only a single entity that was said to have struck a bargain with Kazuya. During Tekken 2, Kazuya still possessed a good side (represented by Angel) which fought Devil for control of Kazuya's soul. However, after Kazuya was defeated by Heihachi at the conclusion of Tekken 2, Devil fled Kazuya's burning body and attempted to possess Kazuya's son, Jin. After being defeated by Jun Kazama, Devil disappeared, only to resurface over a decade later after Jun's disappearance. The Devil branded Jin with a tattoo on his shoulder and later possessed the young man's body after Heihachi attempted to kill Jin. This brought forth the entity known as Devil Jin.

When Tekken 4 was released in 2001, there were a few changes to the concept. For the first time, the "Devil" was referred to as a gene that could be passed along from father to son rather than a mere supernatural entity. Secondly, the Devil within Kazuya somehow resurfaced, now completely merged with its host (Angel is nowhere to be seen), and announced that Jin's Devil is "half" of the original entity. This introduced the concept that the Devils that possessed Jin and Kazuya are somehow operating independently of one-another, instead of being one single entity as originally suggested.



Jinpachi
Jinpachi Mishima, the eldest Mishima introduced to the series thus far, is stated to also be possessed by a "Devil" in Tekken 5. Heihachi states in his own Story mode that Jinpachi has "Devil Blood" and the circumstances by which Jinpachi becomes possessed (his own imminent death) are similar to those surrounding both Kazuya and Jin. In addition, within Jinpachi's ending (viewed when the player is defeated by Jinpachi and chooses not to continue), the text displayed at the conclusion states that Jinpachi is consumed by "the devil".

Heihachi
Heihachi Mishima, son of Jinpachi and father of Kazuya, lacks any evidence of a Devil Gene. The reason for this is a matter of some debate, stemming from the contradictory information surrounding the Devil Gene. Either Heihachi does not have the Devil Gene, or he has somehow managed to avoid activating it.

Yet, despite not being seen with one of his own, Heihachi does have a use for the Devil Gene. With samples taken from Ogre's tissue, he has learned that combining the Devil Gene with Ogre's DNA will allow him to finally create the ultimate lifeform that he seeks. The connections between the Devil and Ogre are as of yet unknown.