Centuries of seeding Mars with moss and cockroaches to warm the planet leave humanity facing the Terraformars, towering humanoid roaches that slaughtered the first crews sent to clear them. To fight back, U-NASA sends teams through the M.O. Operation, splicing insect and animal DNA into their bodies to gain monstrous combat traits. Akari Hizamaru, born with traits inherited from a crew member of the earlier BUGS 2 mission, joins the Annex I expedition, where each soldier's grafted power is all that stands between them and being torn apart on the Martian surface.