In the near future, a mineral known as "Japanium" is discovered under Mt. Fuji. This ore is discovered to produce a powerful energy source known as "Photon Energy". Dr. Kabuto Juuzou and his associates have begun researching Photon Energy, planning to use it as a solution to the energy crisis plaguing the earth, when the nefarious Dr. Hell and his associate, Baron Ashura attack his lab. Along with this, the mysterious "Kurogane House" also has begun to become entwined with the affairs of these two parties. During all of this, Juuzou's grandchildren, Kouji and Shirou, encounter one of Baron Ashura's robots on its way to attack Dr. Kabuto's mansion, where he has begun work on his greatest invention. Dr. Kabuto, seeing the danger at hand, sends out the Pilder to Kouji, allowing him to combine with the giant robot, Mazinger Z, to fight against Dr. Hell's forces.

Source: Wikipedia

AniDB | ANN | AnimeNfo | MAL | TVDB | Wiki (en)

Alternative version: Mazinger Z