''Gyo'' is a {{Seinen}} horror manga by Creator/JunjiIto, also known for creating ''Manga/{{Uzumaki}}'' and ''Manga/TheEnigmaOfAmigaraFault'' (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 [[NinjaPirateZombieRobot undead walking fish.]]

It gets worse.

An animated OVA for the story was released on February 15, 2012 by Ufotable. There are some [[AdaptationDistillation 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 [[PragmaticAdaptation better adaptation]] or a [[AdaptationDecay poor rendition of Gyo]] is up to interpretation.

Trailer for the OVA can be viewed [[http://www.youtube.com/watch?v=Ur_WqzyJj_U here.]]
!!''Gyo'' contains examples of:

* AndIMustScream
* BodyHorror: A particularly gruesome moment when [[spoiler:they tried to remove the tubes out of Kaori's mouth. Her mouth was grotesquely disfigured and judging by the [[{{Gorn}} 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 [[TearJerker sad]].
* BodyOfBodies: Becomes a commonplace sight.
* BrickJoke: The first walking fish is smashed and bagged, [[spoiler: but its bacteria keeps producing enough gases to make it ''float to the mainland.'']]
* CassandraTruth: The fact that Kaori even goes into full-blown fits over a scent only she can smell didn't help.
* CircusOfFear: The setting of the penultimate chapter. Yes, there are clowns.
* CreepyUncle: Tadashi's uncle, also a MadScientist.
* DepopulationBomb
* [[spoiler:DownerEnding: Apart from the hero meeting up with LaResistance, it's a total downer.]]
** [[spoiler: The OVA tries to make the ending [[FromBadToWorse 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 [[spoiler: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.]]
* EditorialSynaesthesia: Stink lines.
* {{Everybodys Dead Dave}}: [[spoiler: Tadashi is the only named character we know for sure survives.]]
** In the OVA, [[spoiler:Kaori is this.]]
* EvilHand: One of the legged machines is removed from the fish it was fused to, after which it latches onto a scientist's arm. Though he promptly [[LifeOrLimbDecision amputates it]] ''it starts crawling around for a while.''
* EvilSmellsBad: Basically what the story is about.
* {{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. The OVA also has its share of the shower scene as well.
** FanDisservice: [[spoiler: 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...]]
* FateWorseThanDeath: Ignoring the physical BodyHorror for a bit, the bacteria slowly paralyses the victims' muscular and nervous systems, keeping them vegetative but very much alive. [[spoiler: Kaori is even conscious enough to reactivate her walker and try to MurderTheHypotenuse.]]
* FogOfDoom: Envelopes the setting pretty quickly.
* ForScience: The apparent motivation for [[spoiler: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.
* {{Hot Scientist}}: Ms. Yoshiyama.
* {{Just Before the End}}
* KarmicDeath: The soldier who shoots at [[spoiler: the legged machines driven by human bodies, and then gets impaled by one.]]
** In a sense, the karma goes even deeper than that, as the Imperial Japanese Army - the predecessor of the JSDF - was the organization that created the bio-weapon in the first place.
* MadScientist: Tadashi's uncle.
* MeaningfulName: "Kaori" comes from Japanese words referring to smell, and she has a very powerful sense of smell (causing her to pick up the Death Stench before anyone else).
* MaybeMagicMaybeMundane: 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.
* NoBiochemicalBarriers: 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.
* NinjaPirateZombieRobot: Zombie fish. With robot legs. [[spoiler: Actually, just robot legs. Made by ghosts]].
* RaisingTheSteaks
* SceneryGorn: The final chapter plays this to the extreme, with giant walkers composed from mountains of dead bodies.
* ScreamingWoman: Kaori. [[{{Narm}} In nearly every scene]]. In the anime, however, she is noticeably much calmer.
* SpiderTank: All the walking fish are fused with these. They steadily get bigger to carry bigger bodies.
* {{Threatening Shark}}s: Walking ones, with spider legs. An early terror.
* TimeSkip: Invoked when the hero falls into a canal and goes into a ConvenientComa for a month.
* ZombieApocalypse: The ending.
!!!Tropes from the OVA:
* AlienSky: A grey, swirling sky is shown off throughout the OVA. [[http://i.imgur.com/RiDIz.jpg It's actually pretty by the end.]]
* AThreesomeIsManly: Erika and her two strangers.
* BlandNameProduct: In the OVA, Tsuyoshi uses a [=BloodBerry=].
* BloodierAndGorier: The manga had very little blood; the OVA has ''gallons''.
* BloodSplatteredInnocents: At one point in the OVA, Kaori slips and falls in a large puddle of blood.
* TheDogBitesBack: Aki to Erika [[spoiler:once she's been infected.]]
* FinalGirl:[[spoiler:In the anime, where Kaori is the only named survivor.]]
* GivingThemTheStrip: Kaori sheds her sneaker to escape when she steps on a vacant set of walking-legs.
* HeavyVoice: This, combined with VoiceOfTheLegion, is a side effect of [[spoiler:Erika's]] infection.
* MadnessMantra: Aki chants "Die, die, die, die" under her breath as she simmers over Kaori leaving and Erika engaging in a threesome.
* MonumentalDamage: The world's doom is sealed with a montage of swarms at the Eiffel Tower, Taj Mahal, Empire State Building, and Kremlin.
* {{Spared by the Adaptation}}: [[spoiler:Kaori]] in the anime.
* UnreliableNarrator: Erika and her gentleman friends are less than truthful in their television interviews.
* VoiceOfTheLegion: This, combined with HeavyVoice, is a side effect of [[spoiler:Erika's]] infection.
* WolverinePublicity: There's quite a few of those landsharks crawling around in the OVA.