Set in the near future where Mother Nature has decided to fight back against all of the human encroachment. Vines and foliage entangle cities, as large wooden mech-like creatures called Arethusa rampage through cities. Souma Shin, a punk kid out of Japan, comes to visit his brother Ken. But all hell breaks loose as Shin finds a group of small kids being used for military purposes, and tries to save them in the confusion created by an Arethusa invading the compound.