A Decisive Battle!! Flaming Hell Castle!.
After Mazinkaiser is dumped into Mount Fuji by the Combined Mechanical Beast, it pursues Boss, Sayaka and the other members of the Photon Power Lab. Before it can kill them it is struck by a massive lightning: the Great Hero, Great Mazinger has returned! While Great battles the Mechanical Beasts, Jun arrives and takes the group to the hidden fortress where Kouji discovered Mazinkaiser. She explains that she and Tetsuya discovered and explored the base, uncovering another Great Mazinger. This Great is far more powerful than the one Tetsuya piloted in the previous episodes and is described as Shin Great Mazinger (New Great Mazinger). The original Great Mazinger was the prototype version made by Dr. Kenzo Kabuto. At that time, Dr. Juzo Kabuto, thought to be dead, was secretly making the final version of Great Mazinger in his underground laboratory. He was also able to finish Mazinkaiser as his ultimate masterpiece. They also uncovered Kaiser Scrander, the wings of Mazinkaiser. Unknown to the unconscious Koji at Mt. Fuji, his Pilder has activated an automatic homing signal, which will activate the Kaiser Scrander. Diving into Mount Fuji, the Scrander docks with Mazinkaiser and the now complete Mazinkaiser emerges from the volcano. After briefly assisting Great, Kouji decides to attack Dr. Hell's base, which was uncovered when he launched his entire Mechanical Beast army. Great Mazinger faces the Mechanical Beast horde as Kouji arrives on Dr. Hell's island and is confronted by Baron Ashura, now rebuilt into a Mechanical Beast. After a long and difficult battle, Kouji emerges triumphant thanks to Mazinkaiser's Final Blade and thoughts of his friends and family. Dr. Hell attempts to win Kouji over to his side and when the hero refuses activates the island's self-destruct sequence. Unluckily for the villain, his escape craft is caught in the explosions as well, while Mazinkaiser emerges unharmed from the inferno.