In the near future, a secret society, Nematoda, with ambitions of world domination, hired three men, Professor Akitsu, Professor Himuro, and Professor Wakatsuki, to build the ultimate "G-Class" giant robot, Zeorymer. Nearly two decades later, on his deathbed, Professor Akitsu tells his son, Masaki Akitsu, that Zeorymer must not awaken. A short time later, a new student transfers into Masaki's school, named Miku Himuro. She quickly persuades him to meet her adopted father, Professor Himuro, and Masaki is curious to find out what is going on, and what his father meant in his final words. Traveling by a high-speed pod hidden under the city, he meets Professor Himuro in a vast underground facility. Nematoda's General Golshid, aware of the Himuro's appearance in Japan, send a G-Class robot to assault their base and kill them, as they believed they had the only "Joint". Himuro compels Masaki to pilot Zeorymer and save them, as he is the only one that can pilot it. Once he agrees, Himuro and his daughter head to an operating room without Masato's knowledge, and he installs a sphere called a "Dimensional Joint" - a flawed duplicate of the original - into his daughter's womb, and she is teleported to within Zeorymer's "eye". This is necessary to utilise Zeorymer's true abilities - without them, it is simply an outdated G-Class robot. Though Masaki stumbles with the unfamiliar systems, Zeorymer eventually awakens fully, Masaki undergoes a strange and short-lived shift in personality, and with the spherical energy weapon on the back of Zeorymer's hand, destroys its opponent in a single attack.