Bisco and Jabi continue their journey through Touhoku in search of Sabikui, the Rust-Eater, a mushroom said to cleanse away any rust. Milo also realizes that if he could cure his sister, Pawoo, if he had this Rust-Eater. Meanwhile, the governor of Imihama, Kurokawa, burns with an unusual obsession with killing Bisco.

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.

Bisco falls into Tetsujin's reactor, taking Kurokawa down with him. The reactor begins to overload, with Milo and the others just barely escaping in time as the dome starts to collapse. However, they're given no time to grieve their loss of Bisco before their next trial assails them. With Bisco gone, Milo tries to figure out what he can do on his own now.

The revived Testujin advances, destroying everything in its path. If this goes on Japan will once again be swallowed up by Rust... After inheriting the spirit of Bisco, Milo resolutely takes a stand against Testujin. Jabi, Pawoo, and Tirol race to his aid and they manage to corner the rampaging Testujin, but...