History Manga / Parasyte

* DoubleMeaningTitle: ''Parasyte'' is titled 寄生獣 (''Kiseijū'') in the original Japanese, literally meaning "Parasitic Beasts". On the face of it, this refers to the PuppeteerParasite alien species which appears among humanity and begins to prey on humans. At the same time, however, it refers to the theme of humans being a threat to themselves and the earth through overpopulation and environmental destruction. Toward the end, the leader of the parasyte conspiracy, Takeshi Hirokawa, accuses humanity of being the real parasites by destroying the Earth, performing a TitleDrop by calling humans "parasitic beasts".

* AsteroidsMonster: The Shapeshifting {{Blob Monster}}esque parasytes can separate into fairly small fragments.

* AxCrazy: [[spoiler:Uragami]], who [[spoiler: is shown remembering how he got captured, which includes visuals of some of his victims, one of whom he raped after he decapitated her]].
* BioAugmentation: Shinichi gains superhuman powers after Migi heals his heart using his own blood.

* BeCarefulWhatYouWishFor: Early on, Shinichi wishes [[spoiler: that Migi would fall asleep forever,]] and when he finally seems to in the end, Shinichi is devastated.

** Shinichi very briefly goes into Blue and Orange ''insanity'' when he decides that [[spoiler: humans have no right to kill an organism just because it's harmful to humans and no right to impose human values on parasytes. He changes his mind after coming to the conclusion that all he can do is act as a human and protect humans, though at this point in his CharacterDevelopment, he pities Gotou more than hates him, and finally reluctantly finishes him off]].

* CarFu: [[spoiler: Migi tries it on Gotou to no avail.]]

** Earlier in the story when Migi met another parasyte that had succeeded in possessing its host, it mentions that Migi should move off of Shinichi's body and into his right hand. Migi wonders if it's really possible. [[spoiler: The BigBad Gotou turns out to be a mass of parasytes in a body, with two capable of controlling them all as the head.]]
** When Gotou escapes from city hall, he is shown to have two bullet wounds where Yamagishi and his troops shot him. [[spoiler: In the final volume, hoping it's the tiny chink in the armor he's been looking on, Shinichi stabs him there with a metal rod -- the rod was covered with poisonous pollutants, leading to Gotou's defeat.]]
* ChickMagnet: Shinichi is depicted as one. His crush Murano obviously likes him. On a trip, he meets a girl on a boat who, later on, keeps following him around and seems to be interested in him. Kana also develops a crush on him after sensing that he's not totally human and begins to keep an eye out for him wherever she goes [[spoiler:with the help of her special powers, which allow her to sense whenever he's nearby.]] She also dreams about him in a sort of white knight scenario in which he saves her from monsters and they embrace; she remembers this dream as [[spoiler: she dies and chuckles, remarking that it's too embarrassing to talk about.]]

* DeliverUsFromEvil: After giving birth, [[spoiler: Tamura starts to take on increasingly human traits, eventually becoming driven to protect her child at any cost, even when it means laying down her life.]]

* EarnYourHappyEnding: [[spoiler: Shinichi goes through hell and back and is forced to witness several brutal, traumatizing deaths, but in the end the parasytes have pretty much stopped killing humans, and he finally gets to be with Murano.]]

* GaiasVengeance: Reiko Tamura [[spoiler: (at least in the beginning)]] [[spoiler:and the totally human Takeshi Hirokawa]] believe the parasytes were created to cull the human population to preserve the earth.

* HopeSpot: [[spoiler: Migi finally agrees to allow Shinichi to let Kana in on the loop about the nature of Parasytes. She dies before he's ever able to do so.]]

* ItCanThink: The first few parasytes seen are slow-witted and relatively dumb, but as the story goes on, the parasytes quickly display the ability to learn and adapt to their circumstances, not to mention prioritize their actions. This is particularly the case with Tamura, whose scientific bent allows her to anaylze situations and perform experiments [[spoiler: such as Gotou]], and even [[ApeShallNeverKillApe sacrifice other parasytes to ensure her own safety and well-being]].

* MamaBear: [[spoiler: Tamura]] of all people managed to pull this on Kuramori when he [[spoiler: made a move like he was about to drop her baby off a cliff; after she stabs him, he says he's surprised that she actually cared enough about her son to act, and she says that she's surprised too. She takes it as far as possible when she cradles her son to her chest and shapeshifts to shield him from harm when the cops get there and begin to collectively fire on her; she simply takes the bullets unmovingly to avoid the chance that her son might be hit, and before she dies, she hands him off to Shinichi and asks that he find a good human family to take care of him. Once he agrees, [[GoOutWithAStyle she peacefully dies with a smile on her face.]]]]

** Shinichi, the protagonist of the series, even goes as far as to call this trope into question, deciding towards the end that humans have no right to hold other species to their values. Though adjusts his view quickly to clarify that he does still have to [[spoiler: put Gotou down,]] he still lets go of any malice against the parasytes.

* {{Ronin}}: [[spoiler: Shinichi fails the university entrance exams due to missing so much school, and has to study and catch up in the epilogue. Fortunately, Muraro is there to help.]]

* TenMinuteRetirement: Kuramori emphatically decides to opt out of further investigation after witnessing a parasyte battle firsthand. He's just an ordinary human -- he has a wife and child, and the whole thing is just not his fight. [[spoiler: Little late for that. [[TheCallKnowsWhereYouLive The parasyte syndicate goes after him,]] but they flub it and kill his wife and child instead; this causes him to be thrown back into the conflict when the police question him to find out what happened.]]

* TinMan: Played with: the parasytes all claim to have no emotions, but in truth it's actually more complicated. They generally lack empathy and are cold and expressionless, but some such as Gotou seem to have something akin to bloodlust. As for human emotions, many feel them, just less strongly than humans; they apparently can (with time) develop complex personalities and emotions. This is evidenced by [[spoiler: Tamura protecting her son with her life and Migi sacrificing himself for Shinichi's safety and internally thanking Shinchi for his friendship -- he even says that he's glad he didn't succeed in taking over his brain.]]

* WainscotSociety: Hirokawa's group of parasytes function a lot like a mafia. Hirokawa serves as the mundane mayor of a city and establishes feeding areas where dead humans can safely be disposed of. When a parasyte kills [[spoiler: Kana]] out of town and Shinichi kills him, they let it go because the guy was clearly a dangerous fuckup, but when Shinichi kills one of their own in the dining garage, it's an act of war and Tamura has to reluctantly give the go-ahead to wax him.

** The interesting thing in the original version is that there are two Japanese words for "parasite" that are used in the series. The less common one is used when referring to the creatures, but the common one is used only once, [[spoiler: when Tamura refers to humans themselves as the parasites of planet Earth.]]

* NerdGlasses: Shinichi has these from the start. [[spoiler: When Shinichi wakes up after Migi heals his heart, Shinichi tries putting his glasses on and realizes he now has perfect vision without them. This is the first hint that Shinichi's physiology has changed dramatically.]]

* TooDumbToLive: [[spoiler:Kana’s final fate. She ignores Shinichi's warning against trying to detect and follow him using her "power," since in her infatuation she's convinced herself that she'll be able to tell the difference between Shinichi and another Parasyte. It turns out she can't, and when she walks in on a hostile Parasyte instead of Shinichi it impales her through the body. Since she's a baseline human in all other aspects, she has lost too much blood to be saved by ANY means by the time Shinichi finds her.]]

* TooDumbToLive: [[spoiler: Kana’s final fate. Her “power” confuses a hostile Parasyte for Shinichi, and she ends up being impaled. And that is her only power of any kind, as otherwise, she is a baseline human. And sure enough, by the time Shinichi finds her, she has lost too much blood to be saved by ANY means.]]

* MamaBear: [[spoiler: Tamura]] of all people managed to pull this on Kuramori when he [[spoiler: made a move like he was about to drop her baby off a cliff; after he stabs him, he says he's surprised that she actually cared enough about her son to act, and she says that she's surprised too. She takes it as far as possible when she cradles her son to her chest and shapeshifts to shield him from harm when the cops get there and begin to collectively fire on her; she simply takes the bullets unmovingly to avoid the chance that her son might be hit, and before she dies, she hands him off to Shinichi and asks that he find a good human family to take care of him. Once he agrees, [[GoOutWithAStyle she peacefully dies with a smile on her face.]]]]

* MamaBear: [[spoiler: Tamura]] of all people managed to pull this on Kuramori when he [[spoiler: made a move like he was about to drop her baby off a cliff; after he stabs him, he says he's surprised that she actually cared enough about her son to act, and she says that she's surprised too.]]

* TinMan: Played with: the parasytes all claim to have no emotions, but in truth it's actually more complicated. They generally lack empathy and are cold and expressionless, but some such as Gotou seem to have something akin to bloodlust. As for human emotions, many feel them, just less strongly than humans; they apparently can (with time) develop complex personalities and emotions. This is evidenced by [[spoiler" Tamura protecting her son with her life and Migi sacrificing himself for Shinichi's safety and internally thanking Shinchi for his friendship -- he even says that he's glad he didn't succeed in taking over his brain.]]

* LastStand: The battle at city hall is this for Hirokawa's parasytes. Ironically, [[spoiler:Yamagishi and his troops -- the men who eliminated the aforementioned parasytes -- end up in a [[LastStand last stand]] of their own against Gotou]]."

* MamaBear: [[spoiler: Tamura]] of all people managed to pull this on Kuramori when he [[spoiler: made a move like he was about to drop her baby off a cliff; after he stabs him he says he's surprised that she actually cared enough about her son to act, and she says that she's surprised too.]]

** Averted when Shinichi's beaten [[spoiler:Gotou, and the pieces of his body are trying desperately to reunite, which Migi estimates only has a 50% chance of succeeding]]. At this point in his character development Shinichi has developed empathy towards the parasytes and hakes it clear that it's NothingPersonal before finishing him off, thereby also nicely averting OnceIsNotEnough because he makes ''sure'' that he's dead.

* DiagonalCut: A parasyte's organic AbsurdlySharpBlade can cut through a human so quickly and cleaning that they'll have time to get scared before they realize they're already dead.

* CrazyEnoughToWork: {{Invoked}}. When [[spoiler:Migi and Shinichi split up to fight Gotou]], Migi pretty much thinls "This is an extremely reckless strategy, but that means Gotou is unlikely to anticipate it."

** [[spoiler:Shinichi and Satomi are happily together, and she's now in college; however, because of all the school he missed while fighting the parasytes, Shinichi either didn't apply or didn't get into college yet, and will take another year to catch up with Satomi (but she agrees to help him study for the entrance test.) Tamura is dead, but she ultimately sacrificed her life to save her baby, which allowed Shinichi to feel emotions again. Detective Hirama assures Shinichi that if the boy is fully human, he will see that the baby is adopted by a loving family, and since Tamura assured Shinichi that he was, it's safe to assume that Tamura's last wish, that he be taken in by good humans and raised well, is coming true..]]

** Every Parasyte is driven to eat humans by nature, even though Tamiya Ryoko proves that they can survive by eating a diet similar to that of humans.
--->'''Tamiya''': “Flies know how to fly without being taught. Spiders know how to spin webs without being taught. Why is that? Here’s what I think: Flies and spiders are simply following an order. I believe all lives on Earth have received orders of some kind. Don’t humans have any directive? When I took over this human’s brain, I received a directive. It said, Devour this species.”
** Migi and Jaw are the sole known exceptions of their species as they never took over a human brain nor do they need to eat for sustenance. They get all the nutrition they need directly from their hosts' bloodstreams.
* HorsebackHeroism: Shinichi, in Kana's dream.
* HumanityIsInfectious: [[spoiler:Ultimately the case with the surviving parasytes. After enough time passing as humans, they stop thinking of themselves as nonhuman.]]
* HumansAreFlawed: Going hand-in-hand with the subverted GreenAesop, this is Shinichi's view at the end.
* HumansAreTheRealMonsters: Sort of touched on. Some of the more socially-conscious parasytes at least believe this is the case.
* ImpostorExposingTest: The military figures out a way to use an x-ray machine to detect parasytes among humans. Before that a simpler method was devised in which you pluck a hair off the head since, in the case of a parasyte, the ambulatory but non-sentient cells would writhe before dying.
* ItCanThink: The first few parasytes seen are slow-witted and kinda dumb, but as the story goes on, the parasytes quickly display the ability to learn and adapt to their circumstances, and prioritize their actions. This is particularly the case with Reiko Tamura, whose scientific bent allows her to anaylze situations and perform experiments [[spoiler: such as Gotou]], and even [[ApeShallNeverKillApe sacrifice other parasites to ensure her own well-being]].

** When [[spoiler:a Parasyte kills and takes over Shinichi's mother]], Shinichi becomes hellbent on taking it down.
** Averted when he's beaten [[spoiler:Gotou, and the pieces are trying desperately to reunite, which Migi estimates only has a 50% chance of succeeding]]. He's about to leave him like that and let luck decide his fate, but instead makes it clear that it's NothingPersonal before dispatching him, thereby also nicely averting OnceIsNotEnough, because he makes ''sure'' that he's dead.
* KillingIntent: Comes up a few times, aside from humans giving a DeathGlare, parasytes can send out a powerful killing intent that animals can sense keenly to the point where birds will suddenly fly away and even a lion is intimidated. When the parasytes do it there's an image of some kind of bug behind them like a mantis or a tarantula. Fitting in that bugs are way more terrifying hunters and killers than mammals as, unlike mammals, they feel no emotion and are biologically programmed to be effective killers where mammals can feel emotions and hunting skills are usually taught to offspring by parents.
* KillItWithFire: Strangely averted here, as practically everything else gets used - dismemberment, impaling, gunfire from [[FiveRoundsRapid bullets]] to shotguns, and on one occasion, ''[[ImprovisedWeapon a rock]]''. Flamethrowers are briefly considered, but rejected. [[spoiler:After Gotou has proven nigh-invulnerable to the weapons that Yamagishi and his troops had been using to great effect against other parasytes, Yamagishi's last thoughts are that maybe a flamethrower would have done the trick.]] The one time it's used [[spoiler:(Shinichi's plan to hit Gotou with a flaming spear while Migi takes off his head)]] fails.

* LackOfEmpathy: All of the Parasytes. Shinichi goes through this for a while after he's partially merged with Migi. Migi and Tamura eventually get a little better about this as well.
* LastStand: The battle at city hall is this for Hirokawa's parasytes. Ironically, [[spoiler:Yamagishi and his troops -- the men who eliminated the aforementioned parasytes -- end up in a [[LastStand last stand]] of their own against Gotou]].
* LaughingMad: Tamura, upon discovering [[spoiler:she's starting to take on human traits]].
* LeaningOnTheFourthWall : When a report on the parasytes is given as "''In a way that everyone will be able to understand''", and a page later when some "Obvious" information is delivered; one character negates by thinking "''I did not know that''"
* LifeOrLimbDecision: Invoked. Shinichi tourniquets his own arm and prevent Migi from reaching his brain -- and it's just the first chapter.

* ALighterShadeOfBlack: While the parasytes are ruthless mass murderers that want to take over humanity, they are definitely much better in comparison to [[spoiler:Uragami. In fact, some of the parasytes even develop human emotions over the course of the series]].

* MamaBear: Tamura of all people managed to pull this one on the detective when he threatened her child.
* {{Masquerade}}: The parasytes try to maintain one, but it breaks down very early. The government, meanwhile, is less about "Masquerade" and more about "information control," releasing information to the public as needed to avert panic.
* MoreDakka: About ten men shoot [[spoiler:Gotou]] with assault rifles, shotguns and a grenade launcher at the same time. Then even more later, up to 53 people. [[spoiler:[[NighInvulnerability He doesn't care.]] See also CatchAndReturn.]]

* MundaneUtility: Shinichi using Migi to deliver the ultimate FastballSpecial in chapter 24 counts as this.
* MySensorsIndicateYouWantToTapThat: Migi. He even shapeshifts into a [[GagPenis gargantuan penis]], in public, because of this.

* OffWithHisHead: Parasytes tend to go for the head, whether they're infecting (X-rays of the host bodies reveal they have no skulls) or just feeding.
* OhCrap: The parasyte who [[spoiler:took over Shinichi's mother's body]] has several during its fight against Shinichi, who is able to follow and dodge its movements, something that should not be possible for a normal human
* PaperThinDisguise: Normally averted by the parasytes, but Uda's parasyte attempts this by giving him a ridiculous jawline when he and Shinichi have to kidnap detective Kuramori
* ParanoiaFuel: [[invoked]] The police's efforts to keep a full-scale public panic from happening should the parasytes' existence become known are a minor but recurring plot point.

** The titular parasytes may be sapient creatures who see their human hosts as nothing more than livestock to kill, devour, and impersonate. But they are not Always Chaotic Evil for it, nor are they treated as such by the story; instead, they operate under Blue-and-Orange Morality, at best being logical, ruthlessly pragmatic beings who only do what they do because it is how they survive as a species in the first place. Some chose to engage in symbiosis with ther hosts, but only when they are forced to do so in order to survive, and some even learn human emotions and empathy over time. In fact, the only outright evil characters seen throughout the series are a handful of ordinary humans.
** Shinichi, the protagonist of the series, even goes as far as to call this trope into question, deciding at one point that humans have no right to kill or impose their values on the parasytes because of the above facts. Though he later grows out of this mindset, he still doesn't hold any malice against the parasytes he fights and protects people from.

* PlayingPossum: [[spoiler:Jaw made Shinichi's mother's parasyte think it was dead, and waited before finishing it off from a sneak attack from behind when it was distracted.]]
* PoliceAreUseless: Played straight early on, when the cops are just as clueless about what's going on as the rest of the country. By the end of the series, however, they've learned all about parasytes, come up with a method of testing to reveal their presence, and developed completely ruthless tactics to kill them.
* PowerPerversionPotential: Averted, Migi's ability to turn Shinichi's hand into a giant penis or mass of writhing tentacles never comes up (as by the time our hero's in a relationship, [[spoiler:Migi's asleep for good]]).

** [[spoiler:This actually emphasises two important things. Firstly, how desperately the fight against Gotou is going, and secondly that Migi is becoming increasingly human in their mannerisms, including possibly expressing emotions like frustration and fear.]]
* PrimalFear: Shinichi can unconsciously cause people to experience this, especially when he's being threatened.

* TheQuisling: [[spoiler:The mayor]] was a HumanAllAlong.
* RadiographOfDoom: A large x-ray is used to spot the parasytes near the end.
* RemovingTheHeadOrDestroyingTheBrain: Subverted - taking the head clean off should kill a parasyte, but they can regenerate from most partial injury. Going for the vital organs tends to work better.

* RiddleForTheAges: It's never revealed what the parasytes are, where they came from or why Kana and Uragami could sense them.
* {{Ronin}}: [[spoiler: Shinichi fails the university entrance exams due to missing so much school, and has to study and catch up in the epilogue. Fortunately, Satomi is there to help.]]
* RuleOfCool: The parasytes' ability to distort bodies is pretty damn awesome.
* RuleOfSymbolism: [[spoiler:Reiko]] holding her baby [[spoiler:and shielding it from bullets while the cops are shooting her to death]] starts to [[PietaPlagiarism resemble a certain Virgin...]].

* ShapeshifterWeapon: Parasytes can transform the parts of their hosts' bodies that they've taken over (usually just the head) into...''things'' that can shred human flesh ''faster than the eye can see''.
* ShotgunsAreJustBetter: The task force commander figures out very quickly that a shotgun blast to the heart will ''destroy'' a human heart, and thus kill the parasyte near-instantly. A load of buckshot is also much harder for them to [[ParryingBullets deflect]] than slugs fired individually.

** The Parasytes' body distortion mentioned above seems to be inspired by [[http://www.doc.gold.ac.uk/~mas02fl/MSC101/Vision/Pics/EscherBondUnion2.jpg [=MC=] Escher's 'Bond Of Union']], by way of Creator/JohnCarpenter's ''Film/TheThing1982''.

* ShutUpHannibal: [[spoiler:The soldiers don't wait to the end of Takeshi Hirokawa's speech to shoot.]]

* TheSymbiote: The parasytes can be categorized as either the parasyte type (those that harm their hosts while benifitting) or the mutualist type (those that co-exist with their hosts to mutual benefit). The parasytes that take over humans are obviously the first and can also be parasitoids if they have to find new hosts (parasatoids are different from normal parasytes in that they specifically end up killing hosts) which entails them lopping off the heads of a human and quickly taking the head's place before the body dies. Migi, Jaw, and any parasyte that only takes on a portion of the host's body are mutualists that protect their hosts from harm, while giving them enhanced abilities and while they feed off their host's blood for nutrition, it only results in their hosts needing to take in more calories (eat more) and doesn't cause any serious health conditions.
* TenMinuteRetirement: Kanamori decides to opt out of further investigation after witnessing a parasyte battle firsthand. He's just an ordinary human, not a monstrous superhuman like Shinichi, he has a wife and child, and the whole thing is just ''not his fight''. [[spoiler: Little late for that. [[TheCallKnowsWhereYouLive The Call Knows Where He Lives]] and his wife and child are eaten, causing him to go to the police.]]
* ThemeNaming: "Migi" (Japanese for right) and "Jaw" are named for the parts they're inhabiting in their respective hosts - the right hand and jaw.
* TheyLookLikeUsNow: [[spoiler:As time goes on, the Parasytes become more and more human, until finally there's no real difference between them and ordinary people.]]
* TinMan: The parasyte all claim to have no emotions; in truth it's actually more complicated. They seem to lack empathy and are generally cold and expressionless, but seem to have something like bloodlust. As for human emotions, they seem to have some that they may feel in different degrees, but they apparently can (with time) develop complex personalities and emotions, like Tamura protecting her son and Migi valuing Shinichi's friendship and sacrificing selflessly for him. See TheyLookLikeUsNow for the final results.
* TitleDrop: When [[spoiler:Hirokawa gives his final speech, calling humans "worms - or [[TitleDrop Parasytes]]. "In the original Japanese he calls them parasitic insects (kiseichuu) and corrects himself to parasitic beasts (kiseijuu AKA the Japanese kanji).]] Unfortunately it's not present in the well-known free scanlation.
* TookALevelInBadass: After recovering from the stab wound that pierced his heart, Shinichi can run at what looks like more than thirty miles per hour, jump more than twelve feet high without a running start, and has reflexes that allow him to actually dodge and turn aside parasyte attacks, which are ''faster than the human eye can see''. He definitely leveled up.
* ToServeMan: The parasyte have a subconscious desire to hunt and consume the species they take over, and their preferred hosts are humans (we do see one parasyte which took over a dog eating another dog). The kicker is that they don't actually need to eat humans to survive and can eat normal food, but (most) parasytes don't feel empathy and so don't see humans as different from food.

* UnableToCry: Shinichi finds himself unable to shed any tears after he is turned partly parasyte by Migi, even when [[spoiler:he is forced to kill his own mother, or when Kana is killed by a parasyte. He is finally able to cry again when Tamura's sacrifice for her child reminds him of his own mother]].
* TheUnreveal: As was the case in "The Thing," We never find out where the parasytes really come from (aside from outer space), why they have such an innate killing intent for their host species, or what purpose they serve considering that they can't reproduce to spread their numbers. Some individual parasytes do start to ponder these things, but most don't really care since it doesn't matter to them either way.
* VisualPun: Since Parasytes only feed on the same species they take over, the first Parasyte-dog is seen eating another dog. Which would make it ''literally'' [[CrapsackWorld a dog-eat-dog world out there]].
* VomitingCop: "Don't puke in the crime scene."
* WainscotSociety: Hirokawa's group of parasytes function a lot like a mafia. Hirokawa serves as the mundane mayor of a city and establishes feeding areas for the safety of all of them where dead humans can safely be disposed of. When a parasyte kills [[spoiler: Kana]] out of town and Shinichi kills him, they let it go because the guy was clearly a dangerous fuckup who was operating on Shinichi's "turf," but when Shinichi kills one of their own ''in the dining garage'', it's an act of war and even Tamura has to reluctantly give the go-ahead to wax him.
* WeirdnessCensor: It takes a while before people other than Shinichi realizes aliens are invading, despite the fact on multiple occasions the parasytes shapeshift right in front of many witnesses (such as the incidence when [[ItMakesSenseInContext a pouncing lion is turned to mincemeat in a parasitized man's face]], and witnesses concoct the explanation he somehow managed to hit the lion with an explosive weapon in mid-flight... despite never moving his arms), because everyone always excuse it as a dream, their imagination, or their eyes playing tricks on them. The sudden massive spike in grisly murders around the world is initially believed to be the work of a secret international cult.

** Characters such as Mitsuo, Detective Hirama and Miki just disappear from the story without mention.
** [[spoiler:Happens in-universe to all the parasytes after the raid on City Hall and their existence becoming public knowledge as attacks and sightings of them all but disappear. It's possible that they were all killed off after the police raid Hirokawa's compound. It's possible that they realized that open attacks and attempts to organize against humanity is dangerous for their survival and that they adjusted their diet to eat regular human food. It's also possible that the parasytes adapted to disguise their feedings as more conventional murders.]]
* WhatTheHellHero: When Shinichi detects a puppy that got hit by a car, Migi determines that it would be dead within ten minutes. Sure enough, the puppy dies, but Shinichi doesn't show any emotional attachment or respect to it, and just throws it into the trash bin. Satomi calls him out on it, and the wake up call makes him realize how much he's changed. He gives the puppy a proper burial afterward.

* TheWormThatWalks: [[spoiler:Gotou]] is made of several parasytes, with each controlling a limb.

** The interesting thing in the original version is that there are two Japanese words for "parasite" that are used in the series. The less common one is used when referring to the creatures, but the common one is used only once - [[spoiler: when Tamura refers to humans themselves as the parasites of planet Earth.]]
** And then there's the last one when [[spoiler:Hirokawa gives his final speech, calling humans "worms - or [[TitleDrop Parasytes]]"]]. Unfortunately it's not present in the well-known free scanlation.
* YouAreAlreadyDead: Many humans hit by a parasyte's blade don't realize they've already been decapitated or cut to pieces, which might give them enough time to scream before they fall apart.
* YourApprovalFillsMeWithShame: Shinichi can tell he's not acting normally when Migi tells him that what he's doing is normal for [[TheSpock his species.]]

* AscendedExtra: One of Shinichi's classmates, a girl with glasses named Yuko who briefly appears in the manga, appears as a friend of his in the first episode where she even has more lines than Satomi and her role is expanded more later in the anime.

* EarlyBirdCameo: The first episode of the anime shows [[spoiler:Uragami the SerialKiller at the end,]] long before said character's first appearance in the manga.

But one specific worm goofs it up - he tried and failed to take over the brain of OrdinaryHighSchoolStudent Shinichi Izumi instead ends up stuck inside Shinichi's right arm. Because of this unique situation, Shinichi and the parasyte, who eventually names himself Migi (meaning "right") are sharing the same body, but still possess their own individual intellects. This gives them an edge in battling the other parasyts, who see Shinichi's ability to think independently as a threat. Shinichi also feels compelled to fight other parasytes, who kill and eat humans as a source of food, in order to protect humanity; Migi on the other hand, like most other parasytes, is incapable of emotion and only fights to preserve his and Shinichi's lives. Thus, Shinichi is forced to deal with all kinds of teenage issues while keeping a horrifying secret and having to battle against hordes of enemies who want to use him or kill him.

One night, strange spores fall from the sky onto the earth. Out of them hatch weird little worms that quickly infiltrate human neighborhoods, looking for host bodies. The worms crawl or burrow their way into the head of a human host, transforming it and the brain inside. This effectively kills the victim, replacing the host's personality and intellect with that of the parasite. These parasites have a ravenous appetite for the flesh of the species they take over--in this case, humans.

But one specific worm goofs it up - because its intended target, an OrdinaryHighSchoolStudent named Shinichi Izumi, was wearing headphones, the parasite can't get to his brain, and instead ends up stuck inside Shinichi's right arm. Because of this unique situation, Shinichi and the parasite he nicknames Migi (meaning "right") are sharing the same body, but still possess their own individual intellects. This gives them an edge in battling the other parasites, who see Shinichi's ability to think independently as a threat. Shinichi also feels compelled to fight other parasites, who kill and eat humans as a source of food, whereas Migi, like other parasites, is incapable of emotion and only fights to preserve his own life. Thus, Shinichi is forced to deal with all kinds of teenage issues while keeping a horrifying secret and having to battle against hordes of other parasites who want to use him (like Ryoko Tamiya a.k.a. Reiko Tamura, a scientist and Shinichi's teacher), kill him (just about everyone else) or worse.

Two collections of short stories set in the world of ''Parasyte'', ''Neo Parasyte f'' and ''Neo Parasyte m'', were published in 2016 and 2017. These stories occur during and after the events of ''Parasyte'', showing what became of Shinichi, Satomi, Migi and the parasites.

** The parasites' blades, cutting through people cleanly with almost no resistance.

-->'''Migi''': Parasites can change their appearance easily. Humans won't be able to catch them.\\

* AsteroidsMonster: The Shapeshifting {{Blob Monster}}esque parasites can separate into fairly small fragments.

** Shinichi averts this due to having to spend so much time fighting or fleeing from the Parasites [[spoiler:and it comes back to bite him big time; see BittersweetEnding]].

** [[spoiler:The Parasites' organization is broken, Hirokawa and Gotou are dead, and the violence by Parasites is almost nonexistent. Once again without a "natural predator", it's left unclear if humanity will render Earth completely uninhabitable one day.]]
** [[spoiler:Shinichi and Satomi are happily together, and she's now in college; however, because of all the school he missed while fighting the Parasites, Shinichi either didn't apply or didn't get into college yet, and will take another year to catch up with Satomi (but she agrees to help him study for the entrance test.) Tamura is dead, but she ultimately sacrificed her life to save her baby, which allowed Shinichi to feel emotions again. Detective Hirama assures Shinichi that if the boy is fully human, he will see that the baby is adopted by a loving family, and since Tamura assured Shinichi that he was, it's safe to assume that Tamura's last wish, that he be taken in by good humans and raised well, is coming true..]]

** Parasites eat humans because that's how they survive as a species, and they feel no more guilt about killing the sapient lifeforms who serve as their prey than humans do about eating livestock such as pigs and cows. Most are either incapable of emotion or don't care enough about it to try, so whenever they explain the reasons behind their actions, it's very matter-of-fact. Furthermore, each individual of the species will do anything to ensure its own survival. Migi is frequently baffled by what he sees as Shinichi's irrational human behavior and thoughts, and considers Shinichi's objection to plans he suggests--such as using his classmates as human shields in order to defeat A, or even just pickpocketing money to purchase a cab ride to safety--to be a misguided case of HonorBeforeReason.
** Shinichi very briefly goes into Blue and Orange ''insanity'' when he decides that [[spoiler: humans have no right to kill an organism just because it's harmful to humans and no right to impose human values on Parasites. He changes his mind after coming to the conclusion that all he can do is act as a human and protect humans, though at this point in his CharacterDevelopment, he pities Gotou more than hates him, and finally reluctantly finishes him off]].

** So, you remember [[spoiler:Uragami, the SerialKiller]] the police brought in to help identify Parasites? The one who escaped and disappeared during the big police raid after shooting his handler? He comes back [[spoiler:in the last chapter]].
** Earlier in the story when Migi met another parasite that had succeeded in possessing its host, it mentions that Migi should move off of Shinichi's body and into his right hand. Migi wonders if it's really possible. [[spoiler: The BigBad Gotou turns out to be a mass of parasites in a body, with two capable of controlling them all as the head.]]

* CombatTentacles: Parasites fight by twisting into long whiplike stalks with razor-sharp blades on the end.
* CompositeCharacter: In the live-action adaptation, the parasite known as "A" survives his first fight with Shinichi and Migi so he can take the role of the nameless parasite who [[spoiler:killed Shinichi's mother and took over her body]].
* ContrivedCoincidence: [[spoiler:Shinichi's parents ''just so happen'' to be finishing a holiday in the immediate vicinity of a parasite who, thanks to a series of accidents, needs a new body. The result is that Shinichi's mother is beheaded so her body can be taken over.]]
* CoolOldLady: Mitsuyo.
* CrazyEnoughToWork: {{Invoked}}. When [[spoiler:Migi and Shinichi split up to deceive Gotou]], Migi thinks that "this is an extremely reckless strategy. But that means even Gotou is unlikely to anticipate our strategy."
* CreepyMonotone: How all the parasites talk (except for Uda's). When a human starts speaking this way, it's a tipoff that they've been possessed.
* CripplingOverspecialization: The parasite who [[spoiler:killed Shinichi's mother]] always goes for a OneHitKill by stabbing its enemies in the heart. When Uda's parasite realizes this, [[spoiler:he's quick to protect Uda's heart in anticipation and behead the enemy parasite from behind after being left for dead.]]
* DeathGlare: Being host to Migi gives Shinichi the ability to unleash awesomely powerful glares, representative of people being able to sense how deadly the pair of them are (the series supposes that animals are able to instinctively tell when another animal is more powerful than them and Shinichi and Migi are FAR deadlier than any human).
* DeliverUsFromEvil: After giving birth, [[spoiler:Reiko starts to take on increasingly human traits, eventually becoming driven to protect her child at any cost, even sacrificing her own life to do so.]]
* DiagonalCut: A parasite's organic AbsurdlySharpBlade can cut through a human so cleanly and fast that they'll have time to get scared before they realize they are already dead.
** In Chapter 3, a parasite performs a CleanCut all around him which causes the humans in front of him to fall to pieces right away, but the woman behind him is seemingly left standing. She raises her hands to her head and screams, only for her head and hands to belatedly separate from the rest of her.
** In Chapter 6, Tamaya kills TheChikan who came back to get revenge on her with a single cut. At first his hand comes off and the sight of it makes him freak out, then he turns his head to see the wound opening in his neck, and as his head falls off his eyes are transfixed on the bleeding stump of his neck as if he can't believe what hit him.
* DiscardAndDraw: In a successful effort by Migi to save Shinichi's life, Migi sacrifices part of himself and now has to go into hibernation for a few hours each day, during which time Migi cannot wake up at all and is useless. On the plus side, this incident left Shinichi with superhuman physical capabilities at all times.
* DoesThisRemindYouOfAnything: How did Shinichi prevent Migi from reaching his brain? By tying his earphones' wires into a tourniquet around his own arm. Lampshaded--his parents walk in soon after and ask if he's abusing drugs.
* DoubleMeaningTitle: ''Parasyte'' is titled 寄生獣 (''Kiseijū'') in the original Japanese, literally meaning "Parasitic Beasts". On the face of it, this refers to the PuppeteerParasite alien species which appears among humanity and begins to prey on humans. At the same time, however, it refers to the theme of humans being a threat to themselves and the earth through overpopulation and environmental destruction. Toward the end, the leader of the parasite conspiracy Takeshi Hirokawa accuses humanity of being the real parasites destroying the Earth, performing a TitleDrop by calling humans "parasitic beasts".

* EarnYourHappyEnding: [[spoiler: Shinichi is forced to go through a lot as well as witness the death of many people close to him but in the end the mince meat murders have stopped and he finally gets to be with Murano.]]
* EnemyCivilWar: How [[spoiler:Gotou]] is defeated.
* EvilHand: Subverted; Migi can do a lot of nasty things, but [[BlueAndOrangeMorality isn't really evil]], just focused on self-preservation to the point that he'll let innocent people die, or even try to kill a human if they discover his existence.
* ExpositoryHairstyleChange: Shinichi has one after [[spoiler:he kills the Parasite responsible for his mother's death. He goes back to his first in the end]].
* FakingTheDead: That's how [[spoiler:Jaw/Parasite]] manages to survive the attack from [[spoiler:Sinichi's mother parasite]]. After realizing that its opponent was going for a OneHitKill by trying solely to pierce its host's heart, [[spoiler:it changed the locations of the organs and let itself be hit]]. Afterwards, it just needed to wait for the perfect occasion to do a sneak attack, and its plan worked without a hitch.
* FanDisservice: PantyShot on a woman chopped in half. Later there's a [[ILoveTheDead necrophiliac]] and a [[ImAHumanitarian humanitarian]] moment. At the same time. And then there's also the scene of Uragami [[ADateWithRosiePalms polishing his rocket]] when seeing a pretty girl.
* FeelNoPain: The Parasites are connected to the host body's nervous system so they can sense injuries and negative stimuli but they have no psychological or physiological attachment to the discomfort they feel. As such, they can't be psychologically distressed by the sensations from injuries nor can these sensations affect them physiologically (a large amount of pain can do all kinds of nasty things to a person like shut them down entirely). This becomes evident [[MajorInjuryUnderreaction when Yamagishi blows away a parasite's hand]], where people would normally scream in agony if it happens to them.

* FiveRoundsRapid: Played straight, as most Parasites can ignore bullets. Subverted when [[spoiler:it actually works on Reiko, and after the humans start using high-powered shotgun ammunition]]. DoubleSubverted when [[spoiler:THIS doesn't work on Gotou]].
* ForTheEvulz: Most Parasites only commit atrocities when they ''have to'', only a few of them revel in doing it. Played straight with Uragami, a ''[[HumansAreTheRealMonsters normal human]]'' who enjoys murdering people just because he ''wants to''.

* GaiasVengeance: Reiko Tamura [[spoiler:and the totally human Takeshi Hirokawa]] believe the Parasites were created to cull the human population to preserve the earth.
* GoodEyesEvilEyes: A good way to tell who's a Parasite is by their emotionless gaze. Subverted a few times - some humans have the same look in their eyes as the parasites do. There's also Miki, a parasite who learned how to look and act genuinely human.

* HalfHumanHybrid: Shinichi becomes one when Migi uses some of his body mass to repair the stab wound caused by [[spoiler:the Parasite that took over Shinichi's mother]]. This results in advanced strength and reflexes, and also in Shinichi [[SociopathicHero seemingly becoming more emotionless for a time]].

* HeroicHost: When the Parasites don't kill you by absorbing your head.

* HumanityIsInfectious: [[spoiler:Ultimately the case with the surviving Parasites. After enough time passing as humans, they stop thinking of themselves as nonhuman.]]

* HumansAreTheRealMonsters: Sort of touched on. The Parasites at least believe this is the case.
* ImpostorExposingTest: The military figures out a way to use an x-ray machine to separate a group of mixed humans and Parasites, since the Parasites can make themselves look human from the outside but don't actually have skulls. Before that a simpler method was devised in plucking hairs since, in the case of a parasite, the ambulatory but non-sentient cells would writhe before dying.
* ItCanThink: The first few parasites seen are slow-witted and kinda dumb, but as the story goes on, the parasites quickly display the ability to learn and adapt to their circumstances, and prioritize their actions. This is particularly the case with Reiko Tamura, whose scientific bent allows her to anaylze situations and perform experiments [[spoiler: such as Gotou]], and even [[ApeShallNeverKillApe sacrifice other parasites to ensure her own well-being]].

** After [[spoiler:a Parasite took over Shinichi's mother and came very close to killing him]], Shinichi becomes a bit more ruthless in his pursuit.

* KillingIntent: Comes up a few times, aside from humans giving a DeathGlare, parasites can send out a powerful killing intent that animals can sense keenly to the point where birds will suddenly fly away and even a lion is intimidated. When the parasites do it there's an image of some kind of bug behind them like a mantis or a tarantula. Fitting in that bugs are way more terrifying hunters and killers than mammals as, unlike mammals, they feel no emotion and are biologically programmed to be effective killers where mammals can feel emotions and hunting skills are usually taught to offspring by parents.
* KillItWithFire: Strangely averted here, as practically everything else gets used - dismemberment, impaling, gunfire from [[FiveRoundsRapid bullets]] to shotguns, and on one occasion, ''[[ImprovisedWeapon a rock]]''. Flamethrowers are briefly considered, but rejected. [[spoiler:After Gotou has proven nigh-invulnerable to the weapons that Yamagishi and his troops had been using to great effect against other parasites, Yamagishi's last thoughts are that maybe a flamethrower would have done the trick.]] The one time it's used [[spoiler:(Shinichi's plan to hit Gotou with a flaming spear while Migi takes off his head)]] fails.

* LastStand: The battle at city hall is this for Hirokawa's parasites. Ironically, [[spoiler:Yamagishi and his troops - the men who eliminated the aforementioned parasites - end up in a [[LastStand last stand]] of their own against Gotou]].

* LeaningOnTheFourthWall : When a report on the parasites is given as "''In a way that everyone will be able to understand''", and a page later when some "Obvious" information is delivered; one character negates by thinking "''I did not know that''"

* ALighterShadeOfBlack: While the Parasites are ruthless mass murderers that want to take over humanity, they are definitely much better in comparison to [[spoiler:Uragami. In fact, some of the Parasites even develop a human conscience over the course of the series]].

* {{Masquerade}}: The Parasites try to maintain one, but it breaks down very early. The government, meanwhile, is less about "Masquerade" and more about "information control," releasing information to the public as needed to avert panic.

* NiceJobFixingItVillain: At first Kuramori refuses to help Shinichi fight the Parasites out of fear for his family. However, the Parasites associated with Tamura decide to eliminate him because of his knowledge. The attempt fails, with Kuramori's wife and daughter ending up murdered, turning Kuramori into a grieving, vengeful father and widower with nothing left to lose. Tamura chews out the Parasites responsible because of this.

* OffWithHisHead: Parasites tend to go for the head, whether they're infecting (X-rays of the host bodies reveal they have no skulls) or just feeding.
* OhCrap: The Parasite who [[spoiler:took over Shinichi's mother's body]] has several during its fight against Shinichi, who is able to follow its movements, something that should not be possible.
* PaperThinDisguise: Normally averted by the Parasites, but Mamoru's Parasite attempts this by giving him a ridiculous jawline when he and Shinichi have to kidnap somebody.
* ParanoiaFuel: [[invoked]] The police's efforts to keep a full-scale public panic from happening should the Parasites' existence become known are a minor but recurring plot point.

** The titular parasites may be sapient creatures who see their human hosts as nothing more than livestock to kill, devour, and impersonate. But they are not Always Chaotic Evil for it, nor are they treated as such by the story; instead, they operate under Blue-and-Orange Morality, at best being logical, ruthlessly pragmatic beings who only do what they do because it is how they survive as a species in the first place. Some chose to engage in symbiosis with ther hosts, but only when they are forced to do so in order to survive, and some even learn human emotions and empathy over time. In fact, the only outright evil characters seen throughout the series are a handful of ordinary humans.
** Shinichi, the protagonist of the series, even goes as far as to call this trope into question, deciding at one point that humans have no right to kill or impose their values on the parasites because of the above facts. Though he later grows out of this mindset, he still doesn't hold any malice against the parasites he fights and protects people from.
* ParasiteZombie: The Parasites infest a host's brain and proceed to KillAndReplace them. They're not obviously nonhuman unless they're feeding or fighting, in which case their heads turn into CombatTentacles and mouths with MoreTeethThanTheOsmondFamily.
* PlayingPossum: [[spoiler:Jaw/Parasite made Shinichi's mother's parasite think it was dead, and bid its time before finishing it off when it was distracted by Shinichi.]]
* PoliceAreUseless: Played straight early on, when the cops are just as clueless about what's going on as the rest of the country. By the end of the series, however, they've learned all about Parasites, come up with a method of testing to reveal their presence, and developed completely ruthless tactics to kill them.

* RadiographOfDoom: A large x-ray is used to spot the parasites near the end.
* RemovingTheHeadOrDestroyingTheBrain: Subverted - taking the head clean off should kill a Parasite, but they can regenerate from most partial injury. Going for the vital organs tends to work better.

* RiddleForTheAges: It's never revealed what the parasites are, where they came from or why Kana and Uragami could sense them.

* RuleOfCool: The Parasites' ability to distort bodies is pretty damn awesome.

* ShapeshifterWeapon: Parasites can transform the parts of their hosts' bodies that they've taken over (usually just the head) into...''things'' that can shred human flesh ''faster than the eye can see''.
* ShotgunsAreJustBetter: The task force commander figures out very quickly that a shotgun blast to the heart will ''destroy'' a human heart, and thus kill the Parasite near-instantly. A load of buckshot is also much harder for them to [[ParryingBullets deflect]] than slugs fired individually.

** The Parasites' body distortion mentioned above seems to be inspired by [[http://www.doc.gold.ac.uk/~mas02fl/MSC101/Vision/Pics/EscherBondUnion2.jpg [=MC=] Escher's 'Bond Of Union']], by way of Creator/JohnCarpenter's ''Film/TheThing1982''.
** The idea of the Parasites taking over the government to some degree is most definitely inspired by ''Film/TheyLive''.

* TheSymbiote: The parasites can be categorized as either the parasite type (those that harm their hosts while benifitting) or the mutualist type (those that co-exist with their hosts to mutual benefit). The parasites that take over humans are obviously the first and can also be parasitoids if they have to find new hosts (parasatoids are different from normal parasites in that they specifically end up killing hosts) which entails them lopping off the heads of a human and quickly taking the head's place before the body dies. Migi, Jaw, and any parasite that only takes on a portion of the host's body are mutualists that protect their hosts from harm, while giving them enhanced abilities and while they feed off their host's blood for nutrition, it only results in their hosts needing to take in more calories (eat more) and doesn't cause any serious health conditions.
* TenMinuteRetirement: Kanamori decides to opt out of further investigation after witnessing a Parasite battle firsthand. He's just an ordinary human, not a monstrous superhuman like Shinichi, he has a wife and child, and the whole thing is just ''not his fight''. [[spoiler: Little late for that. [[TheCallKnowsWhereYouLive The Call Knows Where He Lives]] and his wife and child are eaten, causing him to go to the police.]]

* TinMan: The Parasites all claim to have no emotions; in truth it's actually more complicated. They seem to lack empathy and are generally cold and expressionless, but seem to have something like bloodlust. As for human emotions, they seem to have some that they may feel in different degrees, but they apparently can (with time) develop complex personalities and emotions, like Tamura protecting her son and Migi valuing Shinichi's friendship and sacrificing selflessly for him. See TheyLookLikeUsNow for the final results.

* TookALevelInBadass: After recovering from the stab wound that pierced his heart, Shinichi can run at what looks like more than thirty miles per hour, jump more than twelve feet high without a running start, and has reflexes that allow him to actually dodge and turn aside Parasite attacks, which are ''faster than the human eye can see''. He definitely leveled up.
* ToServeMan: The Parasites have a subconscious desire to hunt and consume the species they parasitize, and their preferred hosts are humans (we do see one Parasite which took over a dog eating another dog). The kicker is that they don't actually need to eat humans to survive and can eat normal food, but Parasites don't feel empathy and so don't see humans as different from food.

* TruthInTelevision: Whenever the Parasites attempt to do something like punch a hole in a wall, they will sustain serious injuries. Migi is the only exception because he's the hand itself.
* UnableToCry: Shinichi finds himself unable to shed any tears after he is turned partly parasite by Migi, even when [[spoiler:he is forced to kill his own mother, or when Kana is killed by a parasite. He is finally able to cry again when Tamura's sacrifice for her child reminds him of his own mother]].
* TheUnreveal: As was the case in "The Thing," We never find out where the Parasites really come from (aside from outer space), why they have such an innate killing intent for their host species, or what purpose they serve considering that they can't reproduce to spread their numbers. Some individual Parasites do start to ponder these things, but most don't really care since it doesn't matter to them either way.

* WainscotSociety: Hirokawa's group of parasites function a lot like a mafia. Hirokawa serves as the mundane mayor of a city and establishes feeding areas for the safety of all of them where dead humans can safely be disposed of. When a parasite kills [[spoiler: Kana]] out of town and Shinichi kills him, they let it go because the guy was clearly a dangerous fuckup who was operating on Shinichi's "turf," but when Shinichi kills one of their own ''in the dining garage'', it's an act of war and even Tamura has to reluctantly give the go-ahead to wax him.
* WeirdnessCensor: It takes a while before people other than Shinichi realizes aliens are invading, despite the fact on multiple occasions the parasites shapeshift right in front of many witnesses (such as the incidence when [[ItMakesSenseInContext a pouncing lion is turned to mincemeat in a parasitized man's face]], and witnesses concoct the explanation he somehow managed to hit the lion with an explosive weapon in mid-flight... despite never moving his arms), because everyone always excuse it as a dream, their imagination, or their eyes playing tricks on them. The sudden massive spike in grisly murders around the world is initially believed to be the work of a secret international cult.

** [[spoiler:Happens in-universe to all the parasites after the raid on City Hall and their existence becoming public knowledge as attacks and sightings of them all but disappear. It's possible that they were all killed off after the police raid Hirokawa's compound. It's possible that they realized that open attacks and attempts to organize against humanity is dangerous for their survival and that they adjusted their diet to eat regular human food. It's also possible that the parasites adapted to disguise their feedings as more conventional murders.]]

* TheWormThatWalks: [[spoiler:Gotou]] is made of several Parasites, with each controlling a limb.
* XtremeKoolLetterz: Paras'''y'''te, [[Creator/{{Tokyopop}} Mixx]]'s MarketBasedTitle for ''Kiseijuu''; Mixx used it to refer to the Parasites; Del Rey used the normal spelling to refer to the creatures, but kept Mixx's title.
** The interesting thing in the original version is that there are two Japanese words for "parasite" that are used in the series. The less common one is used when referring to the creatures, but the common one is used only once - [[spoiler: when Tamura refers to Humans themselves as the parasites of planet Earth.]]

* YouAreAlreadyDead: Many humans hit by a Parasite's blade don't realize they've already been decapitated or cut to pieces, which might give them enough time to scream before they fall apart.

* RightForTheWrongReasons: How did the flatfoots finally bring in SerialKiller Uragami? They caught him ''fiddling around with the {{Gorn}} left by actual parasites.''

* CarFu: Migi tries it on Gotou.
* CatchAndReturn: [[spoiler:Gotou to the soldiers.]]
* CentralTheme: What makes a human, human, and what makes a monster, monster? Can a human become monster, and can a monster become human?
* CharacterDevelopment: The series looks into how a human can establish a mind of a monster (Shinichi), while a monster can become more humane (Migi and Tamura).

** So, you remember [[spoiler:Uragami, the SerialKiller]] the police brought in to help identify parasites? The one who disappeared during the big police raid? He comes back [[spoiler:in the last chapter]].
** Earlier in the story where Migi meets another parasite that had succeeded in its invasion, it mentions that Migi should move away from Shinichi and into his right hand. Migi asks if it is even possible. [[spoiler:Later on, the BigBad turns out to be a mass of parasites in a body, with two capable of controlling them all as the head.]]
** When Gotou escapes from city hall, he is shown to have two bullet wounds where Yamagishi and his troops shot him. [[spoiler:It's the same spot where Shinichi will later stab him with the toxic metal rod, leading to Gotou's defeat.]]
* ChickMagnet: TheProtagonist is depicted as one. Murano, his girlfriend(-to-be), obviously likes him. On a trip, he meets a girl on a boat who, later on, keeps following him around. Kana is also continuously stalking him [[spoiler:with help of her special powers]] and [[spoiler:has some sort of white-knight wet dream about him. TWICE]].

* ChuckingChalk: Shinichi's teacher does this twice to him early on. The first time, Migi instinctively catches and crushes it without Shinichi even noticing; the second time, the chalk hits him because Migi had fallen asleep.

** Parasites eat humans because that's how they survive as a species, and they feel no more guilt about killing the sapient lifeforms who serve as their prey than humans do about eating livestock such as pigs and cows. Most are either incapable of emotion or don't care enough about it to try, so whenever they explain the reasons behind their actions, it's very matter-of-fact. Furthermore, each individual of the species will do anything to ensure its own survival. Migi is frequently baffled by what he sees as Shinichi's irrational human behavior and thoughts, and considers Shinichi's objection to plans he suggests, such as using his classmates as human shields in order to defeat A or even just pickpocketing money to purchase a cab ride to safety--to be a misguided case of HonorBeforeReason.

* ButNowIMustGo: [[spoiler:Migi decides to fall asleep permanently at the end of the series.]]

** [[spoiler:The Parasites' organization is broken, Hirokawa and Gotou are dead, and the Parasite race is apparently on the decline. Once again without a "natural predator", it's left unclear if humanity will indeed render Earth completely uninhabitable one day.]]
** [[spoiler:Shinichi and Satomi are happily together, and she is now in college. However, because of all the school he missed fighting the Parasites, Shinichi can't get into college right away and will take another year to catch up with Satomi.]]
** [[spoiler:Migi allows himself to be absorbed into Shinichi, having apparently come to finally understand and admire the human empathy and curiosity he once disdained.]]
** [[spoiler:Jaw and Mamoru Uda continue to coexist peacefully, to the point Jaw is going a bit senile.]]
** [[spoiler:Reiko is killed by the police, but she ultimately sacrificed her life to save her baby, which allows Shinichi to feel emotions again. Detective Hirama assures Shinichi that if the boy is fully human, he will see that the baby is adopted by a loving family.]]
* BloodKnight: Gotou claims he only lives to fight.

** Parasites eat humans because that's how they survive as a species, and they feel no more guilt about killing the sapient lifeforms who serve as their prey than humans do about eating livestock such as pigs and cows. They are mostly incapable of emotion, so whenever they explain the reasons behind their actions it's very cold-blooded and matter-of-fact. Furthermore, each individual of their species will do anything to ensure its own survival, and they do not understand the human concept of altruism. Migi is frequently baffled by what he sees as irrational behavior and thoughts from his host Shinichi, and considers Shinichi's objection to plans he suggests--like using his classmates as human shields in order to defeat a hostile parasite, or even just pickpocketing money to purchase a cab ride to safety--to be a misguided case of HonorBeforeReason.
** Shinichi very briefly goes into Blue and Orange ''Insanity'' when he decides that [[spoiler: humans have no right to kill an organism just because it's harmful to humans and no right to impose human values on Parasites. He changes his mind after coming to the conclusion that all he can do is act as a human and protect humans, though at this point in his CharacterDevelopment, he holds no malice against the monster he has to kill]].

* BeCarefulWhatYouWishFor: Earlier Shinichi wishes [[spoiler: that Migi would fall asleep forever]] and when he finally does so by the end of the series Shinichi is visibly distraught.

'''Shinichi''': That's why we will chase them down-\\

* ArmorPiercingQuestion: The manga is filled with these. The moral and ethical standards we humans built for ourselves are put to question when a third party enters our paradigm as a mirror to our [[NotSoDifferent inhumanity and savagery]].

* HorsebackHeroism: Shinichi, in Kana's dream.

* KillingIntent: Comes up a few times, aside from humans giving a DeathGlare, parasites can send out a powerful killing intent that animals can sense keenly to the point where birds will suddenly fly away and even a lion is intimadated. When the parasites do it there's an image of some kind of bug behind them like a mantis or a tarantula. Fitting in that bugs are way more terrifying hunters and killers than mammals as, unlike mammals, they feel no emotion and are biologically programmed to be effective killers where mammals can feel emotions and hunting skills are usually taught to offspring by parents.

But one specific worm goofs it up - because its intended target, an OrdinaryHighSchoolStudent named Shinichi Izumi, was wearing headphones, the parasite can't get to his brain, and instead ends up stuck inside Shinichi's right arm. Because of this unique situation, Shinichi and the parasite he nicknames Migi (meaning "right") are sharing the same body, but still possess their own individual intellects. This gives them an edge in battling the other parasites, who see Shinichi's ability to think independently as a threat. Shinichi also feels compelled to fight other parasites, who kill and eat humans as a source of food, whereas Migi, like other parasites, is incapable of emotion and only fights to preserve his own life. Thus, Shinichi is forced to deal with all kinds of teenage issues while keeping a horrifying secret and having to battle against hordes of other parasites who want to use him (like Ryoko Tamiya, a scientist and Shinichi's teacher), kill him (just about everyone else) or worse.

''Parasyte'' was first published in North America by Mixx (now better known as Creator/{{Tokyopop}}), which [[CulturalTranslation Americanized]] every character by changing their names (Ryoko Tamiya was renamed Tamara Rockford, while Migi was "Lefty" because the pages were reversed, for example), censored some sexual elements (though the graphic violence was left untouched), and did away with many Japanese cultural signifiers in the story. Publishing rights were later obtained by Del Rey, who re-released it, reverting the changes Mixx made and using a more accurate translation.

* TheQuisling: [[spoiler:The mayor]] was a human all along.

* TheSymbiote: The parasites can be categorized as either the parasite type (those that harm their hosts while benifitting) or the mutualist type (those that co-exist with their hosts to mutual benefit). The parasites that take over humans are obviously the first and can also be parasatoids if they have to find new hosts (parasatoids are different from normal parasites in that they specifically end up killing hosts) which entails them lopping off the heads of a human and quickly taking the head's place before the body dies. Migi, Jaw, and any parasite that only takes on a portion of the host's body are mutualists that protect their hosts from harm, while giving them enhanced abilities and while they feed off their host's blood for nutrition, it only results in their hosts needing to take in more calories (eat more) and doesn't cause any serious health conditions.

-> ''"''Parasyte'': Because ''Film/InvasionOfTheBodySnatchers'' was for pussies."''
-->-- '''WebVideo/YRulerOfTime'''