If you're looking for anime similar to Gargantia on the Verdurous Planet: Far Beyond the Voyage, you might like these titles.
In the distant future, Earth's oceans have dried up, leaving a vast sandy desert in their place. On this inhospitable planet lives Sam, a boy whose older brother went missing years ago while chasing the sand whale, a behemoth that lurks beneath the sand. Now, Sam has teamed up with the local gang of sand pirates, and has dedicated his life to hunting the whale down himself. But when the boy accidentally rescues a mysterious girl from a fleet of military ships, little did he know that she'd be connected to his long lost brother...
Following a global war and climate change, 35% of Earth's land mass has sunk into the ocean. In this difficult time, countries rely not on armies but on private military corporations to provide security against constant terrorist attacks. One such company is Arqon Global Security, whose staff of mercenaries is tasked with protecting Daiva City on a pay-per-mission basis. Armed with motorcycles that transforms into weapon-wielding mecha, these "blademen" are none too popular with the people they protect - but they always get the job done!
In the year 2050, a violent earthquake on the moon spontaneously changed the moon’s atmosphere and gravity, making it habitable for humans to live upon. Fifty years later, the young Daichi Haruka heads to the moon for summer vacation; he wants to try out his newly created Jetboard, but he wants even more to catch a glimpse of the rabbit person recently spotted in the desert. After running across a little girl with furry ears and her like-bodied grandmother V-May, Daichi finds himself in the middle of a grand adventure! With the help of the giant mecha Granzort, his new companions and two other children, Daichi will help put a stop to an evil monster race that is dead set on controlling the universe!
In the neutral city A'koba the Baralant military uses robot gladiator fights to test battle robots before they are used in real wars. Chirico Cuvie a previous Red Shoulder from the Melkia military and some friends are trying to steal jijirium from Karman Tomus a former technological officer from the Melkia military. Chirico needs it to save his woman, Fyana who is a Gilgamesh PS. Karman Tomus is also looking for the PS Fyana. When Fyana is kidnapped Chirico is forced to fight the local robot battle champion, Niva and the Balarant military who is trying to create their own PS. Niva has a personal grudge against Red Shoulders because he was beaten by them at the fields of Orom. Niva was tried turned into a PS, and thus also hates Fyana. Niva turns Fyana against Chirico and the fight gets much more difficult, since Fyana must not be harmed.