The first episode begins in medias res, depicting the climatic final battle between the Photon Power Lab and Dr. Hell's forces. Meeting the attack head on are the Mazinger Corps and the Kurogane house, who attempt to stand their ground against Dr. Hell's three armies, led by Baron Ashura, Count Brocken and Viscount Pygman. As the battle is being waged we find out that the protagonist Kouji has been missing, and is shown to be in an unknown location, for unknown reasons. While there he meets a variety of strange beings including Zeus. By the time he returns, Dr. Hell's forces have already defeated most of his comrades and Kouji prepares to defeat Dr. Hell, for their sake.

The beginning shows a wrecked Mazinger Z slumbering away from the Dark General. This will be the continuation of Episode 26, where the Dark General comes and Mazinger Z uses the Big Bang Punch to ram the Dark General. The story moves back to the very start of the events which lead to the previous episode. Kouji and his brother, Shiro, are living with their grandfather, Juzo, while mysterious murders occur around their manor. Investigating these murders is Inspector Ankokuji, who was also hired to be Juzo's bodyguard, while Dr. Hell and Baron Ashura prepare for their first attack on the Photon Power Lab. In the meantime, Boss and his gang kidnap Shiro in order to lure out Kouji and beat him. After Kouji fights Boss, Baron Ashura attacks his household with the gigantic robot known as "Talos", forcing Juzo to send out the Pilder to Kouji and Shiro. Moments later, Juzo activates the product of years of research: the Super Robot, Mazinger Z.

Kouji gradually learns to how to control Mazinger Z, while Baron Ashura quakes in fear and rage at the robot who he/she believes to be Zeus (a being who "betrayed" his/her race, the Myceneans, thousands of years ago). After destroying Ashura's Talos with a devastating Rocket Punch, Baron Ashura vows to take revenge against "Zeus" by sending out two of its most powerful robots : Garada K7 and Doublas M2.

Kouji faces off against Garada K7, still struggling to use the controls. Meanwhile, Detective Ankokuji and Juuzou both attempt to flee from Ashura's troops, all while Juuzou suffers from a serious injury. As Kouji begins to move his fight with Garada K7 into the town of Atami, he manages to knock the mechanical beast into a building, only to see a horrific site: The blood of individuals who were crushed under the rubble. Traumatized and afraid of causing more casualties, Kouji attempts to fire a Rocket Punch, only for it to be deflected. Meanwhile, as Juuzou and Ankokuji are surrounded by Ashura's troops, Juuzou manages to enter a shrine (where Boss and his lackeys are hiding) in order to activate a remote control system, sending the giant fist out to catch both he and Ankokuji, returning them to Kouji and Shiro in Mazinger Z's cockpit.

As the battle with Garada K7 continues, Juuzou shows Kouji how to use the devastating "Rust Hurricane" attack, destroying Garada K7 instantly. Ashura then sends out Doubla M2, who begins to use Photon Energy attacks upon Mazinger Z. The attacks fail, however, as Mazinger Z is revealed to have been made from Super Alloy Z, allowing him to absorb the blast. Juuzou then teaches Kouji one last attack: The deadly "Breast Fire" technique, destroying Doublas with a blast of energy. Kouji, Shiro, and Ankokuji's rejoicing is short lived, however, as Juuzou dies moments afterwords. Infuriated, Kouji chases down Ashura in the Mazinger, grabbing him and nearly crushing him, before Sayaka and her comrades arrive to try and calm Kouji down. Ashura then escapes Mazinger's grasp, causing Kouji to let loose another Breast Fire attack, which Sayaka blocks using Aphrodai A. As Sayaka, and her father, Prof. Yumi, help Kouji to calm down, the plane carrying Prof.