The deep sea is the graveyard of Mazinger Z!!

Synopsis

Ships at sea start coming under attack from a giant tail. When Diana A goes to investigate, she too is hit with a high-voltage electric strike from the tail. The creature behind it turns out to be the Mechanical Beast Possess O II. When Mazinger Z, dragged down to the sea floor, tries to escape the water, the flying fortress Gool cuts off his retreat in an instant. Countless small bombs spat out by Possess O II cling to Mazinger Z and begin tearing apart his Super Alloy Z body. With his friend in crisis, Boss Borot — refitted for underwater operation — rushes to the rescue!