The plot is set in the future. There are a race of aliens, called Hideauze, threatening the Humankind that are living in space. During a battle, Ledo, gets caught with his combat suit (filled with onboard AI named "Chamber"), in a spacial distortion and awakes on a Planet filled with Seas.
Now, I have problems labeling this series as just Mecha. Honestly, that is dumbing it down too much.