Kenran Butou Sai: The Mars Daybreak

Put it in a nutshell, Mars Daybreak (MD) is a rough sketch of all Bones' anime features. And Eureka is a linear heir of MD. So they share lots of elements - a crew fighting against regime, an high-tech awesome ship (that thing did fly even though it's a submarine), mecha, teh genki shounen with brown hair, aliens and other stuff including graphics, orphans and a Green Peace spirit. 

Both Suisei and Mars Daybreak are sci-fi that deal with a planet covered in water and humanity living on ships-the only difference being in Mars Daybreak they have underwater cities. Both protagonists pilot mecha and in both mysteries of the past are uncovered under the ocean. Mars Daybreak and Suisei have a light-hearted comedic side and a darker one with more serious moments, though Suisei's is a bit darker. If you enjoyed the comedy and interaction of the characters, and even the battles in Mars Daybreak, you'll probably enjoy the same with Suise no Gargantia.  

I'm kinda surprised no one recommended this. Outlaw Star is about pirates and a treasure hunt just like Mars Daybreak. To compare the two: Outlaw Star does not technically have "Mechs" but the star ships are sorta mechs themselves. I would say that if Mars Daybreak had the more complex story line like Outlaw Star does they would be mirrors of each other just in different universes. Most of Mars Daybreak seemed to developed the love relationship over the quality of the story line. Outlaw Star develops the story line with a quieter approach to the love interests. Overall I would say Mars Daybreak is the little brother to Outlaw Star.  read more 

The parallels are strong between Mars Daybreak and Gundam seed. There are two opposing ship commands and you empathized with those that the common people are told to fear. The main character also has a best friend that is in the opposing force.  

Both shows are about Mecha (robots), Action and Romance, both have a boy who was living on the streets becoming invaluable when it came to piloting the robots, both are english dubbed so use same or similar english voice actors for both shows so if you liked one you'll definately like the other ^.^ 

Really gifted Mains with the same hair they act the same only Gram (Mars Daybreak) isnt AS dense with the main lady, but he still is with others Sci Fi, Adventure,Action Has the same feeling when you watch them 

Contrary to the usual mech fights in space, in these series the action mostly takes place in the ocean. Which isnt as cool as space, but still worth watching. 

Both feature fast pace action with a main character skilled at piloting mechas, serving an organization in order to protect those they care about. In Macross, it's the SMS against aliens and in Mars Daybreak, it's the pirates of Aurora against other pirates and the Navy. They both also go into some of the daily lives that the main character goes through as part of the organization, and have sub tones of romance and humor.  

Both stories are about pirates and are both sci-fi like, but Mars Daybreak is set well on Mars. Both anime have crew that are not what you would say as normal, but they just put more into it. I find them both to be funny, and the plan they come up with is just out of this world. 

Similar Kind of story with romance, adventure and action.  

In both the MC happens to come across a mecha and without any former training can plot it like a pro and ends up aboard a pirates ship with good hearted crew  

Both share the underwater factor but only Daybreak has mechas in it. Tactical Roar has better battles when it comes to underwater strategy whilst Daybreak gets more action with less brains required results. A bit lost between the mechas and the submarines. Tactical Roar has a bit of a more romance oriented plot along with a grand design for the world whilst Daybreak is more adventure oriented with it's bits of romance. 

Blue Sub takes place on a water covered earth while Mars Daybreak takes place on a water covered mars. Both are in the future somewhat. Both take place primarily in the oceans on submarines. Both have mecha fighting under water. Both have talking creatures that aren't human including but not limited to talking cats and dolphins. Both also leave alot in the open for the viewer to decide. The overall plot is also fairly similar. If you like one you are sure to like the other.  

Both shows are adaptations from the video games. Both are mainly mecha shows with some comedy elements which don't require too much thinking and you just sit back and enjoy them. Both shows have the earth-mars independent from each other, while relations not exactly peaceful. Both shows feature veteran seiyuu Houko Kuwashima as the main female character. Make sure watching ZOE OVA before the TV series recommended here. Plot wise ZOE is better, while Mars Daybreak has some more memorable characters. Both shows are somewhat underrated. 

both are futuristic underwater action/adventure/drama genre. XD 

They are both about mains that can pilot mechas they are both cooks and they both take place in mars they are also very similar stories.