Xam'd

Xam'd are depicted as a mysterious type of being related to what is referred to as "Humanform Weapons". The first Xam'd shown in the anime series is the form that Akiyuki Takehara takes after a strange light enters his body during an apparent suicide bombing on a bus on his native Sentan Island. In the wreckage of the bus, the "bomber" (Nazuna) touches his forehead, where a red gem appears, activating the Hiruko within him that entered his body when caught within the blast and causing a 'mask' to appear on his face. Transformed into a Xam'd, Akiyuki is mistaken for a Northern weapon, a Humanform.

Characteristics
Xam'ds' and Humanforms' forms appear to be made of a combination of organic and mineral elements, though they do not appear to be strictly one or the other.

Creation and Similarities.
Both Xam'd and Humanforms are created by instilling or implanting Hiruko into a human host, and are referred to by some characters in the series (ex. Nakiami) as "symbiotes". The emotions within the human host and the Hiruko symbiote are always struggling to become in tune with each other. It is easy for the human host to lose their identity to their own emotions, given power by the Hiruko, and to the emotions of the Hiruko within them. Any emotional imbalance or loss of focus can cause the host to be overcome by madness, often became the catalyst of transformation and thus, causing the Xam'd or Humanform to completely lose themselves and wreak havoc on their surroundings. Those whom eventually became a Humanform would gain the more monstrous, less humanoid appearance and cannot be reasoned with. The only thing to stopped them was by either killing them to put the transformed human out of his/her mystery or implanting them with a Ututu seed to forcefully revert them to human.

In the case of those whom eventually became a Xam'd instead of regular Humanforms, they would manifests masks that cover their face when they

capable to tune their emotions (at least to medium level in Akiyuki's case and Raigyo in master level),

those whom overcame by madness incapable to do the same. Nakiami takes it on herself to train both Raigyo and Akiyuki, with the help of Madam Tenshin, to retain their humanity and develop a harmony with their Hiruko symbiote.

When Xam'd suffer physical or psychological damage, they begin to crystallize and if uninterrupted, the crystal growth will cover them completely and they will eventually turn to stone. Other living things caught in this process will also be overtaken and turn to stone;  Nakiami has had close calls with this several times.

Purpose of Xam'ds Creations
It is revealed by Sannova that the Xam'd were created to oppose the Hiruken Emperor, in the hope of one 'complete' Xam'd forming, and ultimately defeating him. When a Xam'd becomes complete, becoming at one with their Hiruko, the gem on their forehead turns blue. Raigyo had already accomplished this before Akiyuki met him.

Trivia

 * In the words of the ancients, Xam’d was known as Xam’dyunda (“Guiding Hand”).

List of Xam'd appearing in the series

 * Akiyuki Takehara
 * Furuichi Teraoka
 * Raigyo Tsunomata
 * Kujireka
 * Yango
 * Giant Green Xam'd
 * Hiruken Emperor