Argento Soma

Mecha style and alien invaders similar in some respects to Eva and RahXephon. 

They may not be similar at all as Gankutsuou do not have any action and the story is different. But if you like when the main character use their potential as great and nice person to make revenge which led to his or her downfall then you might like both of this animes. Both animes have the feeling "demon acting as a angel" yet Gankutsuou have a lot more of it and show it in a better way which make Argento Soma less similar or better, anyway I think it may be worth to give Argento Soma a small chance. Some other similarity is that both main characters get a chance to revenge from another character/demon and experience a similar tragedy. Quality wise Gankutsuou surpass everything in Argento Soma except the action and it would be better if you have seen Argento Soma first. read more 

Similar: *Alien - targeting a certain destination and have a similar appearance. *Organization - holding many secrets, using weapons created by alien parts or aliens themselves to fight back. If you like one of them you will maybe like the other one as both are very similar to each other. But Argento Soma do not contain much of the psychological content. 

both are mecha series about a giant living machine that came to earth from elsewhere. both have sibling dynamic. in both one of the parties' goals is revenge. 

Both are similar in that they have sci-fi elements that follow their own set of rules, their main protagonists that are confused about who they are throughout the series, and both have main storylines based upon the ultimate destruction of the world. Both Argento Soma and Casshern Sins also similarly have a younger secondary protagonist who interacts with the main protagonist and helps them discover themselves. Although it isn't labeled as one, Argento Soma has loads of psychological elements like Casshern Sins as well. 

In essence allow to set the viewpoints homage between both cult classic, Each norm represents the hollow difference within underlying context that's resolve true revolutionary have multiple meanings associated in a sense with Oshii’s placeholder 

Both are mecha that focus less on the mecha side of things and more on the character drama and psychological side of the story. They are deep explorations of loss, fate, and forces beyond human understanding. If you are looking for a very personal and existentialist story, either of these are great picks. They might feel a little bit dated, but in my opinion they have both have aged quite well, barring a few animation quirks. They also both have a very bizarre soundtrack which fits their equally bizarre narratives. If you enjoyed one and want to watch another mecha with similarly dark themes, give the other a try.  read more 

both main character are same how evil for good rezen, both are real robot in not so far future 

Nothing similar really, but there are mechatronic robots 

The Design of Mechas is similar, they have the shape of spaceships/airplanes, but they change to robots. big robots