Death Stenches are the main antagonist of the series.
According to research notes from Koyanagi, the Death Stench robots were originally designed by the Japanese government during World War II as a last ditch biological weapon to turn the tide of the war. The robots were designed to release a toxic gas that would make enemy soldiers extremely sick when enhaled. However, before the weapon could be deployed on the battlefield, Allied Forces dropped bombs on the cargo ship containing the Death Stench robots, causing them to sink to a watery grave, or so they thought...
Over time, the Death Stenches began taking aquatic life (fishes, sharks, etc.) that crossed their paths as hosts, turning them into undead, berserk monstrosities. Eventually, the Death Stenches make their way to the shore and begin harassing several land dwellers. Although first seen as a harmless nuisance to the public (with the exception of the Shark, which still retained its predatory instincts), the Death Stenches are later revealed to be undead monstrosities who begin to attack people. By the end of both the OVA and the manga, the Death Stench epidemic has spread throughout the rest of the world, killing almost all of the Earth's inhabitants except for the lead protagonist (Tadashi in the manga and Kaori in the OVA who survived due to being immune to the Death Stench virus) and a small group of survivors.
Death stenches look like a four legged spider with four tendrils and a ribcage like clasp used to capture an infected victim. They possess the common mannerisms of the generic zombie in horror fiction, such as strength in numbers and spreading the infection to other uninfected life forms.
The robots transmit the infectious gases by stabbing their victims in part of the body with the metal stilt legs or the cage like structure (although sometimes the robots will murder a potential host with the former choice). The infection at first starts as small dots on the infected person's skin, which some commonly mistake for acne or warts.
Over time, the victim's body swells to enormous proportions, increasing the victim's weight and body mass. The victims also emit a foul smelling gas that actually acts as a lure toward the Death Stench robots. Once trapped within the robot, its tendrils enter the host's mouth and anus, turning them into a host for the Death Stench. The host, however, is forced to watch as the robot commits atrocities that their minds would otherwise not allow.
If, however, the injured victim amputates the infected limb, then he or she can keep the infection from spreading to the rest of the body, as shown when Koyanagi was forced to amputate his arm after being caught in the robot's clasp.
The gas they emit can also produce an unusual macabre imagery when used for the purpose of entertainment, but whether or not the Death Stenches's creators had intended for this to happen is unknown.
In an unusual note, the Death Stenches can fire a sludge like substance (presumably excrement) at other targets, but it unknown whether this has the same infectious properties as their stilts and clasp.
Like generic zombies, Death Stenches can be easily killed by conventional methods, such as shooting (seen when several soldiers opened fire on several Death Stenches), crushing (When Tadashi/Kaori smashed a smaller Death Stench robot with a dresser drawer), and stabbing. Also, if their host becomes filled with excessive gas, the host will explode, forcing them to find a new host to infect and rendering the robot body useless.
They are not easily fooled by knock off variations of the robots and will attack any artificial creations on sight.
Also, individuals with a unique immunity to mutation (Tadashi in the manga and Kaori in the OVA) are immune to the Death Stench.
- Their design bears some minor resemblance to the Face Huggers from the Alien film franchise. Both latch onto their victims to spread a deadly infection that would eventually kill their hosts and both have side effects that are seldom noticed until its too late.