Realians are a race of artificial humans. A wonder of molecular bioengineering, its biological composition comes in various forms based on need, from carbon based duplicates of real humans to those based on silicon or liquid metal. Many of the Realians onboard the Woglinde were made by Vector Industries, and they are hybrid models with a carbon/silicon base. MOMO Mizrahi is a specially designed Realian.
Since the Miltian Conflict, the alteration of a Realian's emotions is no longer allowed. The only exceptions are for Realians in the military or other dangerous occupations, such as terraforming.
Their basic rights are equal to those of humans and are recognized by law. However, due to the fact that their minds are initialized with a slight bias, all Realians tend to display similar personality traits. This bias is applied not only for the purpose of preventing criminal behavior by Realians, but also in consideration of humans who may feel threatened by their "superiority" (albeit only in certain specialized skills). The Episode I Database makes mention of the superior strength of Realians, noting that the weaponry they use in combat is more akin to that which may be mounted on a vehicle versus what a normal human would carry. (A simplified example would be that a human might carry a .30 caliber rifle, while a Combat Realian would carry a 20mm.)
Several companies manufacture Realians, but Vector makes the basic program (in other words the central nervous system) of all Realians. The program is essentially a black box, and any modification beyond regular maintenance and adjustments can be performed only by Vector personnel. Apparently the materials used to create Realian nervous tissues also act like some kind of intoxicant drug, and people have been known to murder Realians and consume their flesh. Consuming Realian tissue causes DME Addiction, which results in conciderable mental instability, hardening and cornification of the skin, and in some worse cases, death.
Various types of Realians are produced to suit various needs. Observational Realians, like MOMO and the 100 Series units seen in operation onboard the Kukai Foundation's flagship Durandal are designed to interact with the systems of a starship and scan for Gnosis. These models were originally constructed by Dr. Joachim Mizrahi and modeled after his young daughter Sakura Mizrahi, who died tragically many years before the start of Episode I. "Weapons Grade" Realians are manufatured by Vector and sold to the Federation military and normally stationed onboard Federation starships. Civilian models also appear to be manufactured as several Realians looking like 20-something versions of the child-like Observational units have been seen assisting government officals like Representative Helmer of Second Miltia and other GFG delegates. These units are most likely manufactured to be secretaries or other types of personal assistants.
It has been speculated that Realians are the basis in the creation of the 'human' population in Xenogears (initated by Persona after the destruction of the Eldridge). This is only a theory as undoubtedly Xenogears may be reworked to fit into the Xenosaga timeframe.