Without warning in the year 2050, an alien race known only as the Inbit arrive, invade and successfully conquer the Earth. Years later and despite brutal past failures, the inhabitants of Mars Colony send out yet another desperate Liberation Force to try and reclaim their lost home world. The fleet is all but destroyed. However, a lone survivor, Stig Bernard, finds himself on Earth. Gathering a mere handful of resistance fighters, Stig journeys on towards the Inbit's headquarters at Reflex Point in an attempt to gather intelligence and, possibly, discover a way to beat them. (Source: ANN)

The first two episodes are summaries of the TV series, the third one (Crest of Iron) takes place in an alternate universe.

In C.E.75, the fighting still continues. There are independence movements, and aggression by Blue Cosmos... In order to calm the situation, a global peace monitoring agency called COMPASS is established, with Lacus as its first president. As members of COMPASS, Kira and his comrades intervene into various regional battles. Then a newly established nation called Foundation proposes a joint operation against a Blue Cosmos stronghold. (Source: sugoi.co)

Set in a far flung medieval-looking world of Arst, Prince Jordy Volder takes up the fight against the ambitions of the conqueror Marder. Jordy uses the legendary giant robot panzer Galient, which is one of many panzers that have been preserved underground for thousands of years. Using an army of advanced robot panzers, Marder is conquering all of Arst in preparation of his plan for dominance of the Crescent Galaxy. (Source: Wikipedia)