God Mazinger

In the ancient, legendary past, the peaceful kingdom of Mu is under siege by the war-like Dragonian Empire. With a woeful amount of fire power and only a giant statue of a deity to watch over them, the young Queen Aira and her people are no match for the Dorado, the Golden King,and his army of dinosaurs.

But Aira reaches out to someone who can save them, a warrior from another time and place. That person happens to be Yamato Hino, an average though highly athletic high school boy in modern-day Tokyo. At first Yamato think she’s going crazy when he gets messages from a spectral young woman, but she eventually convinces him to take the plunge… through a mystical portal to ancient Mu.

Before the Tokyo teen can get acclimated, Dragonia attacks again, but this time, the dinosaurs and soldiers are repulsed by the giant God Mazinger, now merged with Yamato. Though Mu has achieved it's first victory, they have along way to go, as does Yamato, who will need to over come his own deep character flaws and become a true warrior to save the kingdom and get back home.

(Source: Discotek)

God Mazinger is a manga, anime, and novel series by Go Nagai in 1984. Despite the title Mazinger being present, this spin-off series has no connection to previous series. Instead it is an original story about a young man who ends up in an alternate reality.

While God Mazinger has no connection to the other Mazinger series, it is indeed part of the Mazinger franchise as besides the title and the same author as the other series it is featured in the Mazinger Bible along with other manga such Mazinger (USA) and MazinSaga.

The anime version was originally going to feature 24 episodes and while material was drawn up the final epilogue episode was never shown. Part of the reason is because the air date was removed for the 1984 Olympics, and TMS for some reason decided to cut the epilogue from the show entirely.

(Source: Mazinger Wikia)