Replikas and Machine Servants have unique biology when compared to Gestalts (Humans). The differences widen and narrow depending on the quality and generation of the unit, but they are generally different.

Generations

Older generations are more "robotic", and they become more "organic" the newer they are. As in, the technological elements become less mechanical and more bio-mechanical as technology becomes more advanced.

Compared to a Gen 5 or 6, a Gen 1 or 2 might have more fully cybernetic parts, their shells might be more rigid in places, and their limbs may even be fully cybernetic.

The following table shows typical generational quirks:

Metabolism

Slower than a Gestalts, need less building blocks to keep the body going. Require less food than a Gestalt; able to go a few weeks without food before starvation. Energy retention much more optimized.

Require less sleep than Gestalts (4-6 hours) but still need to sleep in order to function. As Replika brains are majority organic, the way they sleep is largely similar to Gestalts, though they can be 'switched off' via special diagnostic machines by specialized technicians.

Lifespan

Standard expectancy is 10 years across the board due to persona destabilization risk; particularly stable Replikas can be allowed to live up to 20 years but that's the Nation's hard limit. Number of Replikas older than 10 years is in the quadruple digits across the entire system.
Biologically, they can theoretically live just as long as a Gestalt if not longer, provided they receive sufficient maintenance.

Immune System

Much more powerful than a Gestalts. Replikas rarely get sick and infections are very uncommon. Illnesses are similar to Gestalts: flu, cold, and other common illnesses effect Replika due to their Bio-mechanical internals.

Black shell/exoskeleton covering the bodies of replikas, analogous to skin. Exoskeleton is almost fully synthetic, but is able to feel touch and scars over mostly naturally.

Shell is soft and flexible to allow full range of motion.

Certain Replikas have their shells reinforced with different materials, increasing their durability. Bullet-Resistant plating isn't as strong as a cuirass, but can be the difference between a wound or a fatality.

Colored stripes around arms/legs are painted on, and can be worn off.

ABTR - Polyethylene Shell

ADLR - Polyethylene Shell

ALKR - Titanium-Reinforced Polyethylene Shell, Bullet-Resistant Armor Plating

ARAR - Titanium-Reinforced Polyethylene Shell

EULR - Polyethylene Shell

FKLR - Polyethylene Shell, Bullet-Resistant Armor Plating

KLBR - Polyethylene Shell, Bullet-Resistant Armor Plating

KNCR - Polyethylene Shell, Bullet-Resistant Armor Plating

LSTR - Carbon-Fiber Reinforced Polyethylene Shell

MNHR - High-Security Reinforced Armor-Plated Servoshell

SAPR - High-Security Reinforced Armor-Plated Servoshell

SGLR - Polyethylene Shell, Bullet-Resistant Armor Plating

SPTR - Polyethylene Shell

STAR - Polyethylene Shell, Bullet-Resistant Armor Plating

STCR - Polyethylene Shell, Bullet-Resistant Armor Plating

TUBR - Polyethylene Shell

WRNR - Titanium-Reinforced Polyethylene Shell

Legs

Replika legs are entirely mechanical from the knee down, terminating in stump-like "stilts" or "pegs", which are specially designed to allow a Replika to maintain the same amount of balance a Gestalt would possess with their normal feet and toes.

All Replika legs have blade-like "all-terrain claws"—three in the front, one in the back—that can be extended and retracted at will to give them better grip or traction on surfaces unsuitable for their pegs such as: sand, mud, snow, or slippery surfaces like oil spills.

Synthetic organs that largely mirror those of a normal Gestalt's, just manufactured to be at peak average performance as standard. Lungs, heart, liver, intestines, stomach, etc.

Various implants to enhance performance and efficiency, connect to internal readouts, and for other required functions. Examples include an implant to the stomach to improve digestive efficiency and prevent needless waste of calories (vomiting) while still allowing the reflex in the event of a poisoning.

Oxidant

Red in color, more efficient than Gestalt blood, better at transmitting oxygen throughout the body and whatever consequences result from that. Oxidant is toxic to Gestalts; do not give Gestalt's oxidant infusions.

Nervous System / Wiring

Similar to their Gestalt creators, Replika units can feel heat, cold, pressure, discomfort, and pain. Their nervous systems are not simple warning circuits, but a complex bio-synthetic sensory networks designed to make them responsive, adaptable and aware of their own bodies.

A Replika’s wiring mimics a Gestalt's nervous system closely enough that most sensations feel natural rather than artificial. They can tell when a surface is too hot to touch, when the cold is slowing their movement, when a wound is minor or enough to cause issues doing their duties. This allows them to react instinctively instead on relying on diagnostic readouts.

Some units have dulled or specialized sensitivity depending on their purpose. Industrial models may tolerate higher pain thresholds, extreme temperatures, and pressure changes. This does not mean they are immune to the vacuum of space or deep depths of the ocean.

This system is not perfect. Internal damage from crushing, gun-wounds, or just age can cause phantom pain, numbness, false heat, trembling, or delayed reactions. Unlike Gestalts, replacing a limb is much easier.

Musculature

Replika musculature is built from synthetic flesh and myomer fiber bundles. It resembles organic muscle at a glance, but is usually muted grey in color, denser in texture, and darker around major anchor points, oxidant channels, or reinforced areas.

Compared to Gestalt muscle, Replika musculature is more compact and efficient. The fibers are layered in tight artificial bundles, giving most Replikas greater strength than an average Gestalt without requiring bulky bodies.

Myomer fibers contract much like organic muscle, but with more consistent power and less wasted movement. They respond to nerve signals, oxidant pressure, and internal regulators, allowing a Replika to balance raw strength with fine motor control.

Because their muscle tissue is denser, Replikas are often heavier than they look. This extra mass improves stability, lifting power, and resistance to impact, though damaged limbs can become difficult to move if power assistance fails.

Replika muscle can still strain, tear, lock, or overheat under stress. Damaged myomer may twitch, seize, or lose precision, and repairs often require sealing tears, replacing ruined fibers, or recalibrating nerve connections before the limb can function properly again. 

Endoskeleton

Replika skeletons are made of metal and are thus much harder to break than those of a Gestalt, more likely to bend or warp or crack than fully snap.

Skeletons are bright blue in color, except for the skull, which is a dark gray.

EULR - Aluminum

ARAR - Steel

ALKR - Steel

ADLR - Titanium

LSTR - Titanium

MNHR - Carbon-Steel

STAR - Carbon-Steel

STCR - Carbon-Steel

KLBR - Titanium

KNCR - Titanium

FKLR - Titanium-Boron

Face

Artificial dermis on face is the only (human-like) skin on their body, capable of sweating through pores and scar. Genetic element to epidermis, allowing variation in skin tones.

"Face plates" separated into upper and lower, black muscle-like layer underneath epidermis, with gray structure between that and the skull, which is capable of minor facial movements/expressions but lacks things like lips, most of a nose, etc. Eyelids are part of this lower layer, so a Replika with no face can still blink provided the lids aren't damaged.

Face masks connect to the lower face plate, secured directly to the Replika's skull.

Brain

Organic brains with numerous modules, computers etc. that connects it to the mechanical elements of the rest of the body.

Memory banks are a type of solid storage that functions via bioresonance, can be accessed freely by the Replika themselves but cannot be accessed by others or by machines (computers etc.) without bioresonance. Bioresonant-imbued machines can store, upload, edit memories.

Replika memory can be "unreliable", smaller details prove easy to slip through the cracks.

Eyes

Fully synthesized of a mesh material,

Akin to cameras. Project a Heads-Up-Display (HUD) into the Replika's vision.

Audio Modules

Replika auditory systems use synthetic eardrums connected to replaceable audio modules. The outer ear and canal resemble a Gestalt’s, but deeper inside the structure becomes more mechanical, with vibration plates, signal processors, balance sensors, and hardened connectors feeding into the nervous system.

All Replikas have built-in hearing protection. Their audio modules can automatically dampen sudden loud noises, filter pressure spikes, and protect the sensory nerves from damage. This allows most models to stand near gunfire, machinery, alarms, hydraulic tools, or engine noise without immediate hearing loss.

The system does not make them immune to sound damage, only more resistant. Repeated exposure to extreme noise, explosions, pressure changes, or corrupted signal feedback can still degrade the modules over time. A Replika may begin to notice muffled hearing, ringing tones, static, delayed audio processing, or difficulty separating voices from background noise.

Audio modules are considered routine maintenance parts and are expected to be replaced every few months to years. Industrial, combat, and shipboard units may need replacements sooner due to constant exposure to loud environments. If ignored, worn modules can cause gradual hearing loss and uneven sensory input between ears.

Technicians can replace the modules without fully disabling the unit, though the process usually requires temporary nerve isolation and audio shutdown. After replacement, the Replika may need re-calibration to restore proper volume balance, directional hearing, and noise filtering. Poorly calibrated modules can leave a unit hypersensitive, partially deaf, or unable to judge where sounds are coming from.

Replika Technicians are expected to know the inner workings of a replika body in intimate detail. They understand the placement of nerve clusters, oxidant lines, synthetic muscle groups, actuator anchors, spinal wiring, joint assemblies, and the layered systems that allow a replika to move and feel like their Gestalt makers.

Lower-ranking technicians are usually trained for routine maintenance, limb repair, diagnostic, fluid replacement, plain suppression, and basic field stabilization. They can patch damaged wiring, seal leaking oxidant lines, reset sensory feedback, and replace damaged plating or synthetic tissues.

Higher-ranking Replika technicians, especially Gestalts deeply embedded within AEON's structure, know far more. They are aware of persona degradation, memory contamination, emotional drift, and the quiet warning signs that a Replika unit is beginning to destabilize. This knowledge is never shared openly. If a replika technician were to talk openly about persona degradation it could cause persona degradation in most Replika units and might end in summary execution of said technician for leaking confidential AEON documentation.

A skilled technician can remove or replace a damaged limb with surprising ease. Before amputation or detachment, they shut down oxidant flow to the limb, isolate the major nerve bundles, and suppress pain feedback from the affected area. This prevents unnecessary fluid loss, reduces shock, and keeps the unit stable during the procedure. In controlled settings, the process can feel less like surgery and more like disassembly, though the Replika may still experience pressure, numbness, phantom sensation, or emotional distress.

This practice also saves valuable resources. A ruined limb is not always discarded. If the damage is not too severe, it can be sealed, cleaned, repaired, rewired, and placed back into service later. Synthetic muscles can be regrown or replaced. Damaged joints can be rebuilt. Oxidant lines can be flushed and patched. Nerve channels can be reconnected if the core structure remains intact. 

Because of this, Replika repair culture treats bodies as both living things and state property. A limb may belong to a unit in the emotional sense, but to AEON it is also material, inventory, and a salvageable asset. Technicians are trained to preserve as much as possible, not always out of kindness, but because every usable part matters. 

This creates a strange relationship between Replikas and the technicians who maintain them. A good technician can ease pain, restore mobility, and keep a damaged unit alive. A cruel or careless one can make maintenance feel invasive, humiliating, or terrifying. For many Replikas, the med bay is both a place of relief and a place where they are reminded that their bodies can be opened, shut down, and rearranged by someone who knows exactly where to touch.