Midori no Ou  

Verdant Lord, 緑の王 VERDANT LORD

In the near future, Mother Nature is fighting back against human encroachment. The setting is during the apocalypse, but we are witnessing it firsthand as it unfolds. Vines and foliage have overtaken cities, while large wooden mech-like creatures called Arethusa rampage through them. Our protagonist is Souma Shin, a punk kid from Japan who comes to visit his brother Ken. As he arrives at the compound where Ken works, he discovers that a group of children are being used for military purposes and tries to save them amidst the chaos caused by an Arethusa invading the area.