Super Robot Wars is a crossover novel by Dan Tatsuhiko with illustrations made by Ken Ishikawa in 1998 and published in paperback by Kodansha. While primarily a Mazinger story, the cast of Getter Robo manga (with their personalities based on their anime counterparts) are also included as supporting characters with mechs including the Shin Getter Robo appearing.
The Photon Power Laboratory researches an unknown elementary particle dubbed the Chrono Lepton which causes a meltdown with Koji Kabuto and Sayaka Yumi transported into an ill-gotten future ruled by giant robots called Creatures. Getting help from a group of psychics, Koji and Sayaka fight back with a replica Mazinger Z and later assistance from the past including the Great Mazinger and Getter Robo G.
However, when the tides appear to have turned, the Holy Knight Creature Gallahan turns out to be an old enemy of the Mazinger team; the Emperor of Darkness controlling the Grendizer. Utilizing the advanced technology of the fallen Mycenae Empire, Gallahan had conquered the world while waiting for humanity to develop a method to travel back in time to complete the time warp technology to conquer the past. With the Majin Heart Mother, he recreates past enemies of the Mazinger and Getter Teams including the Mycenae Empire, the Dinosaur Empire, and even the Getter Robo and Shin Getter piloted by clones of Musashi Tomoe.
With both groups fighting against these threats and eventually destroying the Shin Getter, Dr. Hell is revived from the wreckage of the Great Marshall of Hell and incorporated into the prototype Mazinger Z that Juzo Kabuto kept hidden away by Paracho (a revived Baron Ashura). Dr. Hell's new form, the Devil Mazinger overwhelms the heroes and even absorbs Gallahan, ready to conquer the past while abducting Dr. Lionel from the Photon Power Laboratory. All hope seems lost until professors Yumi and Saotome bring Koji the newly upgraded Mazinger Z, God Mazinger. God Mazinger is able to counter the negative emotion amplification effects of the Devil Mazinger and after a lengthy fight, manages to destroy the Devil Mazinger.
In the aftermath, everyone is concerned about the future world. Koji however is confident that it can be changed.