Milo and Bisco head toward Touhoku in search of the legendary mushroom, Rust-Eater. After reuniting with their friend, the giant crab Actagawa, Milo struggles with his training to ride the crab, but ends up communicating with it thanks to his kindness. That night the two of them try to rest at the Nikkou War Memorial only to reunite with a jellyfish girl they met in Imihama.

On their way to Akita, Bisco and Milo pass by the sea of Calbero and arrive at a desolate town under threat from the deadly creatures, Flying Blowfish. A town that's also full of children and devoid of adults. Meanwhile, Pawoo encounters a mysterious couple living in some ruins as she pursues the others.

With the information obtained from Tetsujin Town, Bisco and Milo continue to head north. As they make their way through Shimobuki Prefecture, the land encased in snow, they encounter Tirol, nearly frozen to death. With Tirol's aid, the two continue their journey toward their final destination - Konakidani, the land said to contain the Rust Eater.

Milo is left standing at death's door by Kurokawa's traps. Kurokawa has once again captured Jabi, and this time he shares a glimpse of his terrifying plan to utilize Tetsujin, the very same defensive weapon that covered all of Japan in the Rust Wind. It seems like no one can stop Kurokawa, and yet at the very moment Jabi feels that despair, a familiar face appears before Kurokawa...

Tetsujin is heading for Imihama, repeatedly attacking Milo in a fierce assault. Yet just as he's about to be killed, Bisco revives from within Tetsujin. Together Bisco and Milo join forces in the final battle against Tetsujin!