If you liked the Casshern Sins anime, the Anime-Planet community thinks you'd like:
Two siblings, Kiyoko and Tatsuya, live in a future reshaped by a terrorist attack known only as "Twin X". In this terrible new world, advanced technology such as computers and radios no longer function and even the very sky has become something terrifyingly alien. With the siblings' mother dead, they are hunted by loan sharks who want recompense for her debt as well as a mysterious Countess who wants them for her own reasons. Even worse, they are also coveted by their father, the terrorist who caused the "Twin X", Gilgamesh!
Honestly this shouldn't be a surprise to anyone. Both have an extreme and heavy atmosphere to their plots. These anime also have bold and defining artstyles, and also some very interesting music to go along with them.
In a dystopic future, the Mir space station fell from space for an unknown reason -- bringing with it a death sentence for every man on Earth. Women have adapted to the loss and for the most part, are living their lives in peace, but bio terrorism is on the rise and the women of Japan need protectors. Hitomi Landsknecht is the leader of a group of such protectors, but she and her comrades will soon discover the new technology known as "ICE". Mysterious and unknown, it is somehow related to males being born again – an occurrence which may signal the rise of humanity once again. However, the technology may also create a monster and destroy what is left of womankind. Can the remaining females change their destiny or will it be too late?
The year is 20XX. Reploids - thinking robots based on the design of 'Megaman X' - work side by side with humans in relative harmony. Rogue reploids, which are prone to becoming violent for no reason, are generally few and far between; however, an abnormal rise in 'rogue' activity has now swept the city and only two elite Maverick Hunters can save the day - the dynamic duo, X and Zero! As their investigation continues and rogue activity increases, X and Zero can't help but feel they are being deliberately misled. With time running out and rogue reploids on the verge of destroying the city, can our heroes track down and thwart the villain before it is too late?
MegaMan X and Casshern Sins are quite similar even though their stories are different. First off, both of them have a cyborg protagonist who is designed for fighting. (Fighting styles are different though) Secondly, both series feature a world in which cyborgs live alongside with humans, almost as equals. It also seems that the human population has decreased in both of them.
Character desing is also something worth noting, since the main characters (X and Casshern) look very much alike.
Ayato Kamina may seem like an average boy in a devastated world, but after being captured by TERRA, a military organization set on saving the world from the Mu, an alien race set on "tuning" the world, he realizes he is an instrument in deciding the fate of humanity and piloting RahXephon. Not only is Ayato the only person who can control the mecha, but he also has a terrible fate of his own. Holding onto memories of his old life and grasping to keep his own humanity, he must struggle in this new world and realize his true potential with RahXephon.
Casshern Sins wants to combine pretentious mindfuckery with an inspiration drawn from a goofy seventies Saturday morning cartoon; hinging the whole affair on some rather bland characters - with rather dry and uncompelling action sequences. I found the results to be less than ideal.
However if that was your cup of tea or you wanted it to be, RahXephon is basically more of the same, only better.
In the 6th year of the Kan'ei era, people enjoy a time of peace; skilled swordsmen are revered and respected, and their lives are their own. Amidst the tranquility, Lord Tokugawa Tadanaka decides, for his own amusement, to hold a fighting tournament in which real swords are used - though laws forbid their use. In a match to the death two highly-skilled swordsmen face off: the one-armed Fujiki Gennosuke, and the blind Iraki Seigen. As they take their respective stances, flashbacks paint a picture of the duo’s past and battle wounds; and thus, the real story begins...