Teito Klein is a former slave who attends the Barsburg Empire's military academy. Having no memory of his past and the power to wield a rare ability called Zaiphon, Teito is constantly under the scrutiny of his peers - except for his best friend Mikage, the only person he connects with. After seeing and remembering the man who killed his father, Teito tries to kill him and finds himself on the run from Barsburg's military might. Now, with the evil beings known as Kor after his soul, the Barsburg Empire after his blood and only the legendary Seven Ghosts to protect him, Teito must unlock the memories of his past before he ends up as a sacrifice for Verloren, the sealed God of Death.
Six months have passed since Rayne, Hyuga, Angelique and Jade were betrayed by Nyx and watched both him and their mansion burn to the ground. Arcadia is now in ruin, Thanatos is growing stronger, and the Aube Hunters - who have been missing for some time - are now seen as scapegoats for the destruction of the land. With time running out, Arcadia's only hope lies with the now-scorned Aube Hunters and Angelique, the only person capable of saving the land from darkness...
Both shows involve mostly male characters, and deal with tightly bound relationships. There are many emotional issues, and people have to make tough choices/sacrifices. Also, both shows demonstrate the hardship of battling darkness, even within your friends or inside yourself.
Akiyuki lives on post-war Sentan Island, always rushing between the demands of his separated parents and his friends at school. But his carefree days come abruptly to an end when his school bus suffers an explosion, the first attack to plunge Sentan back into war. Akiyuki lives to find himself turned into a Xam'd, a mysterious creature, by the suspected cause of the explosion. Engulfed by Xam'd, Akiyuki is eventually saved by a red-haired girl, Nakiami, only to find himself torn away from those he loves. Now he must work to control and understand the creature within him, all while searching for his family and friends in a world steeped in the secrets and chaos of war.
If you enjoyed X'amd: Lost Memories, you'll very likely enjoy 07-Ghost. Both have common threads of war being the primary driver of the series. Both main characters are teenage boys faced with a personal rebellion, secrets and questionable authority figures attempting to decide their fate. They both gain allies in a rather motley assortment of adults with their own secrets, personalities and agendas, and both face very tough situations where their existing, dear friendships are tested.
I would recommend both ways, as these strong common threads are conduits which place either series as comparable to the other.