Gyo is a Seinen horror manga by Junji Ito, also known for creating Uzumaki and The Enigma of Amigara Fault (which, incidentally, is an extra story in the back of the second volume).During World War II, the Imperial Japanese Army commissioned a secret experiment to create biological weapons. The end result - a deadly bacteria that infected corpses and released nauseous gases, and a walking mechanism fueled by these gases, for the purpose of spreading infection. This plan was averted when the ship carrying the bio-weapon was sunk by American bombers during the war - but the bio-weapon remains active, infecting the sea life and spreading back into Japan in the form of what appears to be undead walking fish.It gets worse.An animated OVA for the story was released on February 15, 2012 by Ufotable. There are some artistic liberties with the OVA story, such as Kaori becoming the protagonist, as well as new side characters to boot. Whether this makes it a better adaptation or a poor rendition of Gyo is up to interpretation.Trailer for the OVA can be viewed here.
Body Horror: A particularly gruesome moment when they tried to remove the tubes out of Kaori's mouth. Her mouth was grotesquely disfigured and judging by the detailed drawing one can plainly see that if you try to yank the tubes away her mouth would stick to it and got peeled off. Surrounding the inner lips were a kind of wires that were sewn in. It was sad.
The OVA tries to make the ending even worse by showing scenes of the infection in different countries, a clear sign that unless an immunity is developed, most of humanity is pretty much screwed.
Unlike the manga, the OVA implies that there is an organized effort by the Japanese government (or its remnant) to evacuate the survivors from Japan, or at least from Tokyo. Similar evacuation efforts may very well be taking place in other countries. Also, the internet is shown to be still functional when Tsuyoshi uploads the plague data.
Evil Uncle: More like callous and really crazy uncle.
Fanservice: Though it somewhat serves a purpose to the plot (washing the smell away), Kaori's shower scene in the first chapter is one of Junji Ito's very, very rare examples (possibly the only example) of nudity that seems partially meant to be eye-candy and not just horrifying. The shower scene is also used to implied that the zombie fish is around, though, but that isn't too scary, at least not more scary than other scenes. This unique case of fanservice is probably due to the quite light-hearted start of the manga.
Fan Disservice: When the Death Stench starts to infect humans some chapters later, there is again a lot of nudity, also of Kaori, but this time, it certainly isn't played for fanservice. The term Squick only scratches the surface...
Fate Worse than Death: Ignoring the physical Body Horror for a bit, the bacteria slowly paralyses the victims' muscular and nervous systems, keeping them vegetative but very much alive. Kaori is even conscious enough to reactivate her walker and try to Murder the Hypotenuse.
For Science!: The apparent motivation for Tadashi's uncle improving upon the design of the old, rusted mechanical legs and constructing the two prototype walkers. What exactly he planned on doing with them is a mystery for the ages.
Ghostapo: Given its nature, the Death Stench may or may not have been related to the Axis Powers' notorious occult experiments.
Maybe Magic, Maybe Mundane: What compels the walkers' behavior. They straddle the line between being a sentient bio-weapon and being literally powered by ghosts. The story provides no definitive answer.
No Biochemical Barriers: The disease can apparently infect anything. It was originally developed to infect mammals, specifically the original plan was to release infected dogs and have them spread it to enemy soldiers, but in addition to this we also see such diverse things as elephants, cattle, pigs and whales, the eponymous fish and sharks and even squid. Then again it is supernatural bacteria.