Kouichi Hayase is a high school student who is often bullied at school, but dreams of one day becoming a hero. After being bullied into buying stuff for his schoolmates, he decides to take a shortcut through a forest, which is when a giant object falls on him. After regaining consciousness, he sees a giant robot in front him and a naked girl lying beside him. He covers her with his jacket, and after waking, she is revealed to have partial amnesia and goes with him to his house. Soon after, other giant robots begins to attack the town. The girl tells Kouichi that they are enemies, and goes into town with the intent of fighting them. Following her, Kouichi encounters his friend, Hideaki Yajima, who plans to use himself as bait in order for the two to get away. After Kouichi reveals his frustration in not being able to do anything, the girl reveals her name, Emi Kizaki, and has him summon a giant robot, known as a Machina called Linebarrel. Though he defeats the enemies with his newfound power, he is shocked when Emi tells him that he is dead.

To find out more about the mysterious spheres the Katou Organization is deploying around the world, Kouichi and company storm one of their bases in South America. However, Yamashita leaves his position in order to help Reiji, only to receive a cold reaction from him.