In order to prove that he is a true hero who has been summoned by a goddess, Schwartz, a high school student who is from Japan just like Tachibana and Jinguuji, has takes on a mission to defeat the living armor which has been attacking tradesmen near the Mercs territory. The living armor only targets magic items, and tries to take Schwartz's holy sword, Gram, and Tachibana's tiara, but...!

In a strange village where the people worship a giant squid as a god, Jinguuji searches for Tachibana, who has been abducted to become a sacrifice, and catches sight of Rue, the elven Premier, who had also been a candidate for the sacrifice. Jinguuji forms an agreement with Rue for the purposes of defeating the giant squid with its demands for beautiful maidens, and suggests a bold plan to accomplish the feat.

Schwartz's great efforts have led to the devastation of the rebel army. Kalm, one of the Demon Lord army's top officers, has been guiding things from shadows. In order to keep her operation moving, she uses Ygraine and Tachibana to activate an ancient weapon called Mehpon. Even as they falter in the face of the weapon's overwhelming power, Jinguuji and Schwartz set out to subdue it. Then Tachibana, who is being manipulated by the Demon Lord's forces, uses Mehpon to attack them...

In an ultimate final battle, Jinguuji must face his best friend and companion, Tachibana, who, under the influence of evil forces, controls a giant battle robot and threatens to destroy the entire kingdom! But before Tachibana can regain his senses, Jinguuji must first conquer his own personal inner demon...