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.

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...