The first of Tadao Nagahama's Romance Super Robot Trilogy. (#2: Chou Denji Machine Voltes V, #3: Toushou Daimos) 
Thousands of years ago, the people of the planet Campbell decided to leave their planet and seek out new worlds to inhabit. One group, lead by the scientist Oreana, landed on Earth, but was delayed from their mission. In the early 21st century, Oreana's group reawakens and begins their plan to conquer the Earth. The only effective defense against the Campbellians' giant biomechanical slave beasts is the super-electromagnetic robot, Combattler V and its pilots. 
(Source: AniDB)

35 years have passed since the battle between Brave Raideen and the Demon Empire and all the other Super Robot battles. Peace has continued through the generations where Reideen has become a long forgotten legend, that is until the peace is disturbed once again from the appearance of 2 Fossil Monsters.
 
Amongst the continuing screaming by the powerless citizens, an eighth-grader girl hears a mysterious voice from a great titan. The girl's name is Akira Saezuri who heard the voice of Akira Hibiki, the legendary pilot of the titan Reideen. Thus a new battle begins.

The crossovers of "Chou Denji Robo Combattler V", "Chou Denji Machine Voltes V", and "Toushou Daimos".

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