Terra Formars: Revenge OVA

The second season of Terra Formars . In Terra Formars Revenge, the crew members of the Annex I continue to fight against Terraformars—the large humanoid cockroaches that evolved from the ones sent to Mars centuries ago. However, far from discovering the cure for the lethal Alien Engine Virus that has been plaguing Earth, the Annex I team have learned that some squadrons have agendas from their own countries. Now, the squadrons must not only fight against the Terraformars for their survival, but also each other in the never-ending battle for international dominance.

During the 21st century, humanity attempted to colonize Mars by sending two species which could endure the harsh environment of the planet to terraform it—algae and cockroaches. However, they did not anticipate the species' remarkable ability to adapt. Now in the 26th century, a lethal disease known as the Alien Engine Virus has arrived on Earth, and the cure is suspected to be found only on Mars. The problem is, Mars in the present is overrun by creatures known as "Terraformars," incredibly powerful and intelligent humanoid cockroaches that mutated from those originally sent to the planet. The Annex I team, consisting of a hundred men and women genetically enhanced with characteristics of powerful organisms from earth, has been sent to Mars on a mission to find the cause of the Alien Engine Virus and to help cure humanity—signalling the start of the crew's fight for survival.

Adaptation of the Bugs 2 arc of the manga. In the late 26th century, overpopulation on Earth is reaching the breaking point, and humanity must find new frontiers. The terraforming of Mars has taken centuries but is now complete. The colonization of Mars by humanity is an epoch-making event, but an unintended side effect of the terraforming process unleashes a horror no one could ever have imagined. After humanity's first manned mission to the Red Planet was lost, a second expedition arrives. The explorers prepare to exterminate the cockroaches that were used to transform the Martian environment. They are shocked to discover that the insects have mutated into giant, aggressive humanoids with one overriding goal — exterminate the humans! But this crew of explorers has each undergone the Bugs Procedure, terrifying experimental surgery designed to make them more than human...

Seeking for revenge, Count Saazbaum, a Martian, attacked the Earth. Later on, the war between the Terrans and Martians ended with Earth's Terrans gaining the victory. However, nineteen months later, the battle between them continues. Martians still continues to invade the Earth and the Terrans to protect it.