Alien invaders take over Great Mazinger who is at the entrance of a museum next to Mazinger Z as symbols of peace. Grendizer fights the evil invaders and Great Mazinger is recovered. 

When the Vegan empire dispatches a new general to oversee the takeover of Earth, he quickly manages to capture Koji Kabuto and, learning of Great Mazinger through interrogation, quickly commandeers it from a museum where it was kept as a symbol of peace. 

It is now up to Duke Fleed aboard Grendizer to stop humanity's former defender from becoming its destroyer.

(Source: ANN)

It is the 25th century. The dark lord has 'infected' history with time-devices that could damage history beyond repair. Flint and his father lived in the prehistorics when they got turned into fossiles. They are discovered and Flint ges turned back to his original state. With the help of his father, a boy Tony and a girl Sara he has to travel trough time to bring the time-devices back to the land of time so history will be saved.

Asahi's life in reality ended simultaneously when she died playing Union, a world-renowned online RPG. The members of Subaru went separate ways when Union shut down due to Asahi's death. Six years later, Haruto logs onto a renewed version of Re'Union and reunites with Asahi who had died. Is it really her or just an electronic ghost? The former team members reunite and enter the mysterious and deadly online game to find out. (Source: TBS Global Business)

The third, Missing Link, deals with the events between Tekkaman Blade and Tekkaman Blade II.