Devilman vs. Hades Series by Go Nagai

A modern sequel to the horror manga classic Devilman! When high schooler Fudo Akira merged with the demon Amon, he became Earth's darkest hero: Devilman. The armies of Hell itself trembled at his name. But not even Devilman could stop the end of the world--nor could he save the woman he loved. Now he must descend to the underworld to bring her back. But first he must defeat Hades, the Emperor of Darkness, no matter what the cost.The epic Devilman/Mazinger Z crossover starts here!