The Hachijo Clan (八条家 Hachijo-ke; Hachijo Family) is a family of assassins that has been made reference to in Tekken 7. The Hachijo's most notable member is Kazumi Mishima; Heihachi's deceased wife. The clan is also a lineage that has possessed the Devil Gene since ancient times, as revealed by a song a journalist hears during his investigation of the Hachijo clan in Kyoto.
For millennia, the Hachijo clan, inheritors of demonic blood in Kyoto, have operated in the shadows, assassinating those who were deemed a threat to the world. During the early parts of the mid 20th Century, Kazumi Hachijo was sent to Jinpachi Mishima's dojo, where she met Heihachi.
The clan saw that Heihachi's ambition would lead to great tragedy across the globe, which proved to be prophetic. And so after five years of marriage, Kazumi would act on the clan's orders to destroy Heihachi, but despite her powers she failed and was beaten by him.
In a last ditch effort to kill Heihachi, Kazumi attempts to kill him from behind, but Heihachi sensed her in time to stop her, holding her by the throat. The demon that was Kazumi attempted to use Heihachi's love for Kazumi to escape his grasp, using the fact that if he went ahead with the deed, he would cause a never ending cycle of hatred. But her efforts backfired; it only enraged Heihachi, leading him to snap her neck, killing her.
However, Kazumi's ghost is still alive and undetected for 30 years, despite having lost her physical body.