Mars Daybreak

Kenran Butōsai Za Māzu Deibureiku, or Mars Daybreak, is a Humongous Mecha anime aired in 2004 by TV Tokyo and licensed by Bandai Entertainment in the US.

The story takes place on a colonized Mars, where nearly the entire planet (save for the peak of Olympus Mons) is covered by a massive ocean (the initial colonization apparently having Gone Horribly Wrong). The people live on floating city-ships, with the planet's abundant water being their primary export. Somehow, the end of the "Pan-Galactic War" has left the planet in the midst of a severe economic depression. Of course, Economic troubles mean crime. And with a planet that's nearly all ocean, that can mean only one thing: Pirates! With the surface under heavy satellite surveillance, the pirates have been forced underground. Or rather, underwater. Instead of sailing over the waves, they lurk under them in submarines. And the baddest pirates around are the crew of the sub Ship of Aurora.

Which brings us to our hero, Gram River: A young man living on the city-ship Adena. While trying to help a friend get out of a bad situation, he ends up in the middle of a raid by the Ship of Aurora, and thrown overboard when the port is rammed and breached. Fortunately, a Humongous Mecha comes out of nowhere and rescues him. Unfortunately, this mech is assumed to be part of the pirates' forces, and is promptly attacked by the local Earth Forces mechs. He is eventually hired on by the crew to pilot the mech.

Naturally, nothing goes that easy, or there wouldn't be much of a series. The first major complication is the fact that Vess, one of Gram's dearest childhood friends, has just been stationed to Mars as part of the Earth Forces, and she isn't happy at all to discover that he's become a Pirate. The other is the initially-unrelated kidnapping of the Granddaughter of the Earth's President, that they get blamed for when they just happen to go after the real kidnappers for their own reasons, and wind up catching them just as they're trying to ransom her, and further complicated when they end up inadvertently recruiting her.

Tropes:

 * A Mech by Any Other Name: Round Bucklers, usually shortened to RB's.
 * All That Glitters: The Treasure of the Aboriginal Martians.
 * The Captain: Elizabeth
 * Cool Boat - The Ship of Aurora.
 * Die Hard On A Pirate Submarine
 * Falling Into the Cockpit: Well, floating, anyway...
 * Hey, It's That Guy!: Itsuki lives with his siblings Kunikida and Kyon's sister on a giant ship!
 * Mecha-Mooks: Earth Force R Bs are remote controlled.
 * Names to Run Away From Really Fast: Subverted with two of the strongest R Bs in the series, named Mermaid and Squirt.
 * Not as much of a surprise given that the other two are named "Vector of Hope" and "Wing of Samurai".
 * Of course Yagami holds this title pretty well, given that his nickname is "Yagami the Shinigami". He backs it up VERY well too given his track record of being able to dismantle multiple enemy round bucklers in a single swoop. He pretty much is pretty much the more experienced version of Graham who is already noted to being capable of taking on multiple round bucklers in his own right.
 * Obfuscating Stupidity: Captain Doolittle to a T.
 * Really 140 years old:
 * Red Baron: Yagami is known as "The Grim Reaper"
 * Rule of Cool: Among the Pirates are a talking Cat and . No explanation is given for their existence.
 * Sapient Cetaceans: Poipoider, a dolphin who spends much of his time in a suit of power armor wielding heavy weapons.
 * Submarine Pirates
 * Talking Animal: Clara and Poipoider.
 * The Only One Allowed to Defeat You: Vess towards Gram.
 * The Pirates Who Don't Do Anything: Kuberness is a partial example. Though he has the loot to back up his pirate-ness, throughout the show he acts more like a mercenary than anything.
 * Uplifted Animals: Cats and Porpoises, apparently
 * Victorious Childhood Friend: Vess.
 * What Do You Mean It's Not Awesome??: The Elizabeth Cannon, which consists of

English

 * Crispin Freeman - Rich
 * Johnny Yong Bosch - Gram
 * Steve Blum - Yagami
 * Yuri Lowenthal - Junior

Japanese

 * Tomokazu Seki - Gram
 * Houko Kuwashima - Vess
 * Tetsu Inada - Rich
 * Daisuke Sakaguchi - Junior