The Tetsujin are a type of Asimovec. Their lineage is very old; the earliest descriptions that are provably Tetsujin date back to the Interplanetary Age. Their origin was in the Pacific Rim area of Old Earth, and they still retain some of that region's culture. The Tetsujin began as multi-purpose/multi-environment labor bots with limited autonomy. Over time users demanded smarter and more versatile robots that could handle increasingly complex functions. This eventually led to the installation of heuristic operating systems with networking functions that allowed individuals to share information with their work groups. The first true Tetsujin spontaneously achieved sapience in 1173 a.t. They were at first sapient as networked groups rather than as individuals (an arrangement similar to that of the Anttechians), but further evolution brought on individual sapience.
Tetsujin differ from many vecs in that they have a standardized body plan that almost none of them vary from. The body resembles a stocky barrel-chested humanoid frame two meters tall and massing 217 kg. The entire body is obviously mechanical; the skin is metallic, the hips and shoulders have ball-and-socket joints, the knees, elbows, wrists and ankles are universal joints and the digits are cleverly hinged. The head is egg-shaped and completely featureless except for a speaker grille in front and a series of audio receivers on either side. The chest is studded with optical sensors whose armored lenses are made of transparent superplastic. There are smaller sensors on the fingertips of the right hand — the lenses/fingernails act as armor for these. The left forearm is disproportionately large and has three visible hatches. Every Tetsujin wears the mon, or heraldic logo, of eir work group/family on eir shoulders. The one concession to individuality that Tetsujin make is in surface coloration. Each individual chooses eir own color and pattern upon reaching the age of majority. Minors are glossy white in all of the optical bands that Tetsujin can perceive, and adults are not permitted to be that color (though they may have it as a base color in a pattern). Many Tetsujin appear to be flat gray until viewed under ultraviolet light; these deceptively bland-looking beings often display bold patterns in that band.
Tetsujin have a number of built-in capabilities courtesy of their machine bodies.
The vocal and auditory systems contain multiple elements. A Tetsujin is capable of producing and hearing sounds ranging from 1 Hz to 37 kHz. The head is devoted entirely to audio reception and processing; decapitation merely deafens a Tetsujin.
The optical systems in the chest can perceive in the radar, infrared, visible light and ultraviolet ranges. The radar and UV systems include active emitters.
The phalangeal eyes on the right hand are limited to the visible and UV ranges but have active emitters for both. Having eyes and lights on their fingertips allows Tetsujin to reach into tight, dark spaces and still see what they're doing. The fingers and palm of the right hand are jointed so that all of the digits are mutually opposable.
Power comes from a pair of radioisotopic generators with solid state active cooling for the cold poles. Main power is augmented with high-energy-density capacitor banks that provide surge power on demand. The main power plants are located in the thighs with capacitor banks and battery backups in the shins and upper arms. A Tetsujin can run for years before needing to replenish its radioactive fuel, but they need periodic radiation decontamination more frequently.
The high-torque electric motors in each joint grant Tetsujin greater strength than that of a baseline human, and their "muscles" never tire.
The left forearm has three retractable armlets that have quick-connect attachment points. This is to accommodate modular systems that vary according to the task at hand. The armlets are usually equipped with tools, but Tetsujin who are travelling in dangerous areas may carry weapons. Many are fond of arc welders, drills or power saws, which serve equally well as tools or as close-range holdout weapons. There is even a confirmed instance of a Tetsujin carpenter mounting a gauss-driven nail gun. Because of the strict limits imposed by the dimensions of the equipment chambers any gear mounted in the tool arm must be of Tetsujin manufacture or built to their specifications. Children are not allowed to carry weapons.
The pelvis contains a ring-laser gyroscope array that provides excellent balance in spite of the uneven mass distribution caused by the left arm. A small high-density counterweight in the right forearm compensates for the oversized tool arm.
Tetsujin were designed to operate in a wide range of environments; they can tolerate greater extremes of temperature or gravity than baselines can and are unaffected by vacuum (they remain vulnerable to corrosive atmospheres, however). Tetsujin enjoy working and living in space; their power plants are much more efficient with a greater temperature differential between the hot and cold poles.
The most impressive Tetsujin feature is the brain, which is located deep in the torso. Like all computers Tetsujin brains process information far faster than an unaugmented organic mind ever could and possess total recall. Their core programming grants them excellent learning capacity and a high degree of adaptability. They also have built-in microwave transceivers that allow data sharing with any other properly equipped unit within range — "radio telepathy" in binary language is the default communication mode among themselves or other sophonts with compatible equipment. Most spectacular is the single design innovation that the Tetusjin incorporated into themselves; the braincase. The brain is completely enclosed within a spherical ceramoplastic shell. Even if an attack destroys the vec's body its brain may survive inside this armor. The inner surface of the braincase is lined with a Faraday cage to protect against EMP attacks.
The technology that goes into making Tetsujin is surprisingly primitive, but they seem reluctant to upgrade it (probably due to their innate conservatism and Asimovec lack of ambition). Having bodies that lack buoyancy makes Tetusjin incapable of swimming. They are sufficiently insulated to resist immersion for brief periods but don't like being underwater. They are also not built for running — even a baseline can easily outpace a Tetsujin — and have slower reflexes than do sophonts with more efficient musculature. The most significant limitation of Tetsujin is the inconvenience caused by their power plants. Tetsujin are forbidden to enter any community that prohibits radiation hazards in populated areas. This restriction applies to most areas with primarily biont populations, so there are a lot of places where Tetsujin can't go.
As vecs Tetsujin are asexual, and they tend to find bionts' sexual behavior amusing. Developing a gender identity is not forbidden but it is considered eccentric. Simulating a gender identity — or allowing oneself to be assigned one — in order to simplify dealing with bionts is perfectly permissible. Tetsujin reproduction occurs on assembly lines. A community typically has a "nursery" in which all members take turns building young. Every adult in the work group is a parent to every child, and all will take part in care and education. A Tetsujin remains a child for 10 standard years — the duration of their presapient ancestors' warrantee — before being declared an adult. The period of minority is spent learning essential skills and in productive labor. All children are expected to contribute labor to the community at least equal to the cost of the individual's manufacture. Those who fail to do so are mind-wiped, reprogrammed and made to start childhood over. Indoctrination is also a major part of adolescence; Tetsujin are drilled in etiquette, heraldry (they can each recognize the mon of any established family on sight) and the creeds of their work groups. Family loyalty is the cardinal virtue of Tetsujin society. A Tetsujin's name consists of the name of the work group followed by a four-digit numerical designation followed by the individual's base color (example: Raichu 0073 Gold, who might be known as Goldie 73 to eir hu friends). A work group will never consist of more than 10,000 individuals; a family that large will not produce children except to replace lost members.
Government in Tetsujin-only communities is full participatory democracy. Every adult member of the community votes on every issue. Anyone who has expertise in the matter at hand may address the assembly before the vote is called. Most matters require only a simple majority, but particularly important situations require a three-fourths majority. In the event of a tie or a lack of clear majority the matter may be referred to outside arbitration (usually to a neutral ai). Legal disputes are handled like any other vote; the entire community acts as judge and jury. Any case involving a serious crime requires a 75% guilty vote to convict. This system seems unwieldy until one considers the Tetsujin file-sharing, fast processing and radio telepathy abilities -- a community of several thousand can disseminate the details of a new law or the evidence in a criminal case to its most distant members within minutes, process the information and return a vote in less than an hour. The efficiency of this system makes it common in vec- or ai-run polities whether or not there are Tetsujin present. The most severe punishment that Tetsujin mete out is exile; the offender is stripped of eir mon and cast out of the work group.
Tetsujin share the common cultural traits of Asimovecs -- they lack ambition and are non-aggressive. They will fight only if they or those under their protection are attacked. Most are content to serve their work groups for life. Even the most adventurous members of the breed indulge their wanderlust by signing up for a term of service. Most Tetsujin who leave their work groups are ship's crew, bodyguards or indentured laborers. Even outcasts will look for some individual or group to serve. No Tetsujin has ever joined a military unit to date, but those who have been enslaved may be sold into the ranks.
Tetsujin are a moderately common Asimovec variant. They are found wherever vecs are welcome and radioactive power plants aren't outlawed. Tetsujin tend to be hu-friendly — not surprising considering their origins — so they are less common in hu-hostile polities. They actively avoid the more violently anti-hu areas. Radiation Nation has made overtures to the Tetsujin but the vecs find that group's radical agenda distasteful. The Tetsujin enjoy friendly relations with Clade Faber (with whom they have several joint colonies) and the Starhand.