Heihachi Mishima reigns as the central antagonist in the anime adaptation. His defining act stems from his son Kazuya's childhood: believing Kazuya's compassion rendered him unfit to lead the Mishima Zaibatsu, Heihachi hurled the boy off a cliff to purge perceived weakness and test his strength, an act provoked by Kazuya comforting young Jun Kazama over a dying animal.

As an adult, Heihachi orchestrated the King of Iron Fist Tournament on his private island, masking his true agenda. He adopted Lee Chaolan, positioning him as Kazuya's rival and tasking him with tournament oversight. Lee served as Heihachi's enforcer, deploying assassins Nina and Anna Williams in repeated attempts to eliminate Kazuya before the tournament ended. Heihachi's ultimate ambition sought global destruction, believing humanity's inherent corruption justified annihilation and replacement under Mishima rule. He aimed to awaken a destructive power within Kazuya, viewing him as the potential successor for this new world order.

During the tournament's climax, following Lee's failures, Heihachi confronted Kazuya. He overpowered his son physically and verbally, revealing the cliff incident was designed to forge Kazuya into a vessel of destruction. When Kazuya succumbed to his inner Devil power but was later redeemed by Jun's intervention, Heihachi attempted to execute them both in a rage. He survived the island's self-destruct sequence, triggered by Lee, escaping aboard his private jet as the compound imploded.

His personality manifested consistent ruthlessness, viewing compassion as a fatal flaw. He openly disdained Lee, dismissing him as worthless after his defeat. Though expressing a twisted respect for Kazuya's destructive potential, this vanished when Kazuya rejected his path, driving Heihachi to try killing Kazuya and Jun without hesitation.