They both have giant robots that are special or unique. They both have a very solemn, monotone, cold main character who are able to drive the robots better than anyone else. Both have a princess from Mars who comes to Earth for political reasons. Both have people who are trying to kill or capture the princess for political reasons. There's war related history and events. People die. People fight. Both have many characters from all different backgrounds that some how add to the story.
Seriously, there are both so similar I'm surprised no one had already suggested them.
A young lady who is an important political figure from Mars, wants to travel to Earth for the betterment of humanity. On her journey she is aided by young people who are brilliant in mecha-fighting, specially the main protagonist who is a calm-minded person and head for the battles without the slightest sign of hesitation or frightened look. Events change and take a surprising turn when the people from Mars betrays the lady, and battle breaks out between our protagonists and the Martians. A lot of deaths occur in these strategic battles as political turmoil among them take a turn for the worse.
There is a core difference though; in MSG: IBO our protagonists are the ones who accompany the young lady on her trip to Earth, where in case of A.Z, the protagonists are from Earth who help the young lady in her survival during the battle. read more
* Child soldiers...
* Both sides uses huge robots/mecha's as the main weaponry...
* Both MC's are combat geniuses....but like every other geniuses they're a little bit cold towards other characters...
* Both have enemies who are trying to kill or capture the princess for political reasons.... (independance)
* Both have really emotional moments at times...
I feel those have the same type of ridiculously powerful, cool main character, taking care of the bad guys while his comrades get slaughtered. Also realistic mecha with suits needing refueling, ammo, and repairs; that goes without saying for gundam. Good looking battle scenes being only a background for greater political schemes and power struggles. Obsolete and forgettable romance threads shoujo style. Gundam gets a lot more character development.
The plot line in both of these shows is nearly identical. However the way the plot progresses and the way the story is told is quite different. Both revolve around a interplanetary society where the higher class of one planet considers those from a different planet to be inferior, despite the fact they are of the same species. In MSG Iron-Blooded Orphans the higher class of Earth amounts that the people on Mars are worthless, and many children are enslaved and forced to fight. In Aldnoah.Zero the ruling class on Mars considers the Earth to be inferior. Both shows involve a Princess traveling to another planet in order to attempt to achieve equality. It's a struggle in both as the ruling hierarchy attempts to thwart the princess in any way possible. Both are quite good in my opinion, and if you watch both of them you will see that the plots practically mirror each other. Both of the shows attempts to shine light on inequality. MSG has more of a serious tone, as it involves child slavery, whilst Aldnoah.Zero is still quite serious but revolves more around a "hero" who happens to be a student. read more
G-Tekketsu has the concept of child soldiers being used as a very prominent plot point. This idea has been touched upon since the very first Gundam series but season 1 of 00 was the first to use it prominently and openly.
In 00, the protagonist used to be a child soldier, part of a religious fundamentalist group called KPSA, and is now part of a different group called Celestial Being who use armed force to pursue a world without war and therefore a world where children do not have to be soldiers like he was.
In G-Tekketsu, the main characters are all child soldiers/slaves working for private security force CGS who take over CGS to become the self-run Tekkadan. Additionally there are other child soldier characters too. read more
Being a part of the same franchise, you can obviously expect a degree of similarity within all Gundam titles. 00 bears most similarity to IBO so far as the characters both possess and are not objected to using the mobile suits right off the bat. some thematic similarities lies within the morality of war and the subject of child soldiers and their exploitation by various religious sects and corporations. the central groups are both militaristic, and respond and act appropriately as you'd expect of such a group, professionally, practically and efficiently.
I know it might seem odd to recommend these two, but hear me out:
-Both are MUCH improved over their predecessors (Zexal and AGE respectively)
-Both are much darker than previous entrees
-Both share Japanese VAs
-Both feature a return to older plot elements (Arc V takes a lot of cues from 5Ds, and IBO takes cues from AWGX, Wing, and 00)
Both series has a main gundam that was created generations before the characters in the story. These gundams are superior in almost every way compared to the other modern mechas in their series and are both piloted by the main protagonists who are on their early teenage years. However, the protagonists are very different from each others in personality such as the protagonist in Iron-Blooded Orphan is stoic child soldier while the one in Turn A is a curious compassionate worker. Both series also has a princess but from different satellites; Iron-Blood Orphans has a princess of Mars and Turn A has a princess of the Moon. Their are also small hints of romance between the main character and the princess in both the series. read more
Both shows involve a young man using a Gundam from a conflict years (or in Turn A Gundam's case, Centuries) ago to fight for an organization. Also, both feature a princess from a planet that isn't Earth.
Like SEED, discrimination against human beings who are not "natural" is a common theme because in both of these series non-natural human beings are so prominent unlike the emergent NewTypes, Innovators and X-Rounders.
In SEED, genetically engineered human beings called Coodinators dominate the space colonies, whereas on Earth, especially in member-nations of the Alliance, Coordinators are referred to as monsters. The discrimination is field by the propaganda of terrorist organization Blue Cosmos who influence nations in the Alliance.
In G-Tekketsu, people who have prosthetics, whether it be the highly advanced Alaya-Vijnana system or something so basic as artificial legs, are also referred to as monsters or at the very most with curiosity. Like Blue Cosmos, the Gjallarhorn promotes the discrimination with its close ties to the nations of Earth. read more
Both plots rely heavily on a "racism" theme as well as changing government and civilian rights. There is also the concept of people "made" to control Mobile Suits. The only difference is that Iron-Blooded Orphans has less action (as in they don't fight in every single episode). But when there is no fighting they are forwarding characterization and introducing new plot pieces.
All in all, Iron-Blooded Orphans reminds me of Seed a lot! It's definitely worth a try :D
Protagonist and deuteragonist are mistreated and abused orphans who have a strong bond and consider each other brothers. Simon and Kamina's dependence, unconditional love, and blind-faith on one another mirrors that of Orga and Mikazuki's.
Together, they create an organization and treat the members of their organization as their family. Members of the organization are dedicated and loyal to their organization and what they stand for, and care deeply for one another. If you like the sense of brotherhood in one series, you'll like it in the other.
Both series deals with systematic oppression on people of lower class and their desire to overturn the inequality.
Basically, they're both anime about sworn brothers who fight for independence with their makeshift family of other brothers in mechs.  read more
-Both are mecha anime, like duh....
-The relationship shared between Orga and Mikazuki in Iron-Blooded Orphans are quite similar to the relationship shared between Kamina and Simon in Gurren Lagann
-Both anime started out with the protagonist being under control of a higher authority.
-Both anime shared a similar background landscape
-The mecha design in both anime are different
-The art style used in both anime are drastically different and both were made by different animation studios.
-The antagonist in both series have different goals in mind
It is an odd recommendation but I can't help but see Blues EXE being similar to Gaelio due to the same VA and both are police who are rivals with the main character. Both are cartoony in some way but have serious moments as well and Rockman has a history of having elements being influenced by anime such as Gundam for example.
Child Soldier and brutal warfare are portrayed in both shows in a dark and gritty format. Mikazuki and Sven are similar of some sorts. Note that the fights are more realistic as opposed to lasers and powers.
NGE and Gundam IBO take place in a post apocalyptic world with deconstructive themes on their perspective genre-mecha. Only difference is that NGE focuses on human psychology and development whereas IBO focuses on politics and corruption. One thing they have both in common is the child soldier concept.
With a cast so huge, it would seem impossible to develop them all in any meaningful way, but these anime manage. The best parts about these shows are the realness of the characters and the cleverness of the plot. Definitely check them out.
If you want a better story with mechas, drama, and politics, Code Geass is one for you. An interesting note is that Mcgillis and Suzaku share the same VA and have similarities once you watch through the whole show.
Both series are darker than the previous series and have to do with survival through wars. I found Mikazuki Augus to be the Gundam version of Emiya Kiritsugu plus his Gundam is similar to Berserker as well.
Both shows are about squadron of soldiers surviving the harsh world and involves young soldiers. Akito's relationship with Leila is similar to Mikazuki with Leila as a nod to Heero and Relena plus they are all based on their archetype. Not to mention that one of the characters in Gundam IBO has the same seiyuu and a similar mecha with a relationship with the other character who too has the same seiyuu.
Both Anime's contain a very strong bond of Brothers In Arms. The fight only for themselves for the most part, and in doing so achieve something greater. The bond is also created in a similar way by means of their social status.
Toward the Terra is like Iron-Blooded Orphans about a group of family like comrades who travel through space to reach the place where they belong. They both very heavily emphasis character development over plot so the story takes a long time to pick up. Both shows are very emotional and touches on issues such as discrimination, survival in a world that has forsaken them, and struggle for a place to call home.
Both series has a main mecha that was created way before the characters in the story are born. These mechas are both remnants of a previous war many years ago and their combat abilities surpass than the other mechas in their respectful series. However, the mechas function are very different in both the series. The ones in Iron-Blooded Orphans functions through the use of energy and fuel while the ones in Break Blade functions through the use of sorcery with crystals. The main protagonist are also different as the one in the gundam is a child soldier while the one in Break Blade is a farmer. Both series also has royalties that appear to be attracted to the main characters.  read more
As both shows have quite the similar elements of space-ships, missions and/or requests from clients, and colonies to planets involved to be the stage of the plot, it works in the premise that Mouretsu Pirates is a seeming much milder, more innocent shoujo-version than the rather ruthless, brutal shounen-genre that is the Gundam: Iron-Blooded Orphans.
Also, both shows have Hisako Kanemoto and Yoko Hikasa as supporting seiyuu-casts on it.
Both feature Gundams from a war in the past used to fight again, with the main character being a member of a crew with a cool starship. Both also have the main character protecting a girl who is a love interest for him.
Both series are heavily themed around people in space wanting to win independence from the Earth - in IBO, it's Mars that's trying to become independent from Earth; in Wing, it's several space colonies.
Both Gundam IBO and the Code Geass franchise tells stories motivated by political turmoil.
Having similar genres and characters (i.e. a strategist/leader and a brilliant mecha pilot), both series are highly recommended shonen epics which will undoubtedly keep viewers on the edge of their seats.
If you flipped the perspectives in AGE (focusing on the natives of Mars instead of the Earth Federation), made the story a "Band of brothers fighting for independence" style story instead of a "young boy discovers the horrors of war" style story and got rid of all of AGE's flaws, you'd pretty much have IBO.