[[quoteright:280:http://static.tvtropes.org/pmwiki/pub/images/BirdyMighty.jpg]]
[[caption-width-right:280:Tsutomu and Birdy]]

Tsutomu Senkawa was an ordinary kid living in Tokyo. Birdy Cephon [[SpellMyNameWithAnS Altirra/Altera/Altaria]] was a beautiful SpaceCop on a mission to stop a plot by alien criminals that involved Earth. One night, during a battle with the alien fugitive Geega, "Berserker Killer" Birdy accidentally attacks Tsutomu, fatally injuring him. To save his life, Birdy has to [[TwoBeingsOneBody merge with him]]. Now, as Tsutomu gets used to sharing a body with a girl, they both have to work together for Birdy to complete her mission.

Called ''Tetsuwan Birdy'' in Japan, it's based on a manga that was started and unfinished in the 1980s by Yuuki Masami. The animation studio Creator/{{Madhouse}} with direction by Yoshiaki Kawajiri of ''Anime/NinjaScroll'' fame made a four-part OVA series in the 1990s that finished part of the plot, but still left loose ends. In 2003, Masami went on to do a reboot, starting the story over from the beginning. The series ended after twenty volumes, and a new series after a time skip called ''Tetsuwan Birdy: Evolution'' is currently running. In 2008, a TV series, ''Tetsuwan Birdy Decode'' (''Birdy the Mighty Decode''), with direction from Kazuki Akani of ''Anime/TheVisionOfEscaflowne'' fame, premiered, and in January 2009, the second season, ''Tetsuwan Birdy Decode 02'' (''Birdy the Mighty Decode 02''), premiered.

''Decode'' can be found on Funimation's Youtube channel [[http://www.youtube.com/show/tetsuwanbirdydecode here!]]
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!!This show provides examples of:
* AccidentalPervert: Tsutomu's dad tries to [[BathtubBonding bond with him in the bathtub]], but finds a naked Birdy in his place.
** An unusual gender-inverted example in ''Decode'', where Hayamyia, after hearing Birdy's voice in the bath, takes a look out of surprise, only to find a naked and embarrassed Tsutomu.
* ActionGirl: Birdy
* {{Adorkable}}: Tsutomu in the OVA series.
* AliensSpeakingEnglish / TranslationConvention: Played with interestingly in this. If examined carefully enough, you see that in every interaction where there is a potential language problem (i.e. a human and an alien), there can be a reasonable expectation that that alien learned Japanese. For example, Birdy was on Earth for 6 months, working in the modeling business. Aliens that wouldn't know Japanese naturally only speak to other aliens (though of course the dialogue is translated for the viewer), so they are speaking their language. Tsutomu can only understand the aliens because his mind is inside Birdy.
* AlternateContinuity: The ''Decode'' series
** Also, the OVA and original manga follow a very similar continuity, while the remake manga follows a similar but different continuity.
* ArtShift: The animation in the second half of the OVA was more cartoony. Also the animation in the seventh and twelfth episodes of the second season of ''Decode'' is looser and sketchier than the rest of the series, but expresses extreme momentum and force in the scenes where it is used.
* AttackHello: Birdy's mentor, Skeletso, does this when Birdy visits headquarters. She reciprocates enthusiastically.
* {{Autodoc}}: Birdy can be seen using tanks with such features to help her heal from battles.
* BadDreams: Shyamalan in ''Decode'', involving fire and explosions. Not that they get him many sympathy points, what with everything he does while awake.
* BathtubBonding: As noted above, Tsuotmu's dad tried to do this with his son, but ended up discovering Birdy.
* BatmanInMyBasement: In the OVA, Tsutomu has to keep his situation hidden from his family. This ended-up making his family think he's crazy as he seems to be yelling to himself, his father (in an attempt at BathtubBonding with his son) [[AccidentalPervert catching a nude Birdy in the bath after she switched with him]], his family to wonder why the son is [[NakedPeopleAreFunny running around the house in the nude]], and his sister accuses him of [[{{Crossdresser}} crossdressing]] when Birdy decides to "borrow" some of her clothes. Averted in ''Decode'', where the sister has moved out and only checks in on him, and [[ParentalAbandonment his parents have left due to the father's job, leaving Tsutomu alone]]. The trope remains in the remake manga, though Birdy has her own clothes for being a little less conspicuous.
* TheBerserker: Birdy, to the point that she's earned the nickname "Berserker Killer Birdy."...though, it bears mentioning, the machine she killed in revenge for Violin's death was known as a Berserker.
** It also bears mentioning that in the remake manga and its currently-running sequel, she goes berserk when pushed enough.
* BerserkerTears: [[spoiler: Birdy's crying these when she's trashing the robot that killed Violin]].
* BigBad: Christella Revi, though more hand-ons in the OVA, but her ''Decode'' self is also the Big Bad, but is more of a [[HeWhoMustNotBeSeen She Who Must Not be Seen]][=/=]TheVoice[=/=][[ManBehindTheMan Woman Behind the Man]].
* BigBadWannabe: Shyamalan. [[spoiler: He falsely believes he's in full control of the Ryunka and wants to use it to destroy everything. He winds up being one of the first victims killed by it at the end.]]
* BigEater: Birdy is one.
* {{Biopunk}}: The society from which Birdy comes has advanced organic technology (for example, their spaceships and some buildings being biological). Their medicine can fix people blown in half, and replace limbs and faces. Beyond that, [[spoiler: Birdy and Nataru are artificial bioengineered humanoid weapons, and the Ryunka is another, probably artificial, biological weapon]].
* BitchInSheepsClothing: ''Shyamalan'', good grief. He's an expert at looking like an open, charming, boyish young executive while plotting to wipe out large chunks of the human race.
* BittersweetEnding: The first season of ''Decode'' [[spoiler:ends with Tsutomu's girlfriend leaving after being separated from the Ryunka, a DoomsdayDevice, and having lost several of her memories]].
** The end of episode 11 of season 2 hints at possibly bringing back some of her memories/romance, as she returns for a visit, and asks Hayamiya about all these pictures of her with Tsutomu (back in season 1), and wondering what they're doing there...
* BloodierAndGorier[=/=]DarkerAndEdgier: ''Decode'', especially season 2.
* BodyHorror
** Geega's transformation into his true form in the OVA involves his real face popping from his neck and part of his real neck inflating before firing a blast.
** Bacillus is an oozing parasite that bonds and kills the host, then moves on to another. [[spoiler: In the OVA, he bonds himself to several dogs at once before before getting repelled by [[MundaneSolution dish soap]], then bonds himself to some MechaMooks that Birdy took out earlier. In ''Decode'', his then-current host falls apart, then moved to Geega, who also falls apart--his flesh seems to be literally melting.]]
** In the OVA, a scientist tries to recreate an old super-soldier project he involved in. His experiments ending up mutating the test subjects into monsters. [[spoiler: One of his test subjects is ''himself''.]]
** In the remake manga, the same scientist's experiments causes his test subjects to mutate into powerful beasts, with strong animal instincts and urges to go with it. [[spoiler: One of Tsutomu's classmates becomes a subject after he's shot, but is saved from being subjugated and learns to control his power. When Tsutomu realizes his sister is also being given the drugs, he and Birdy land the first blow to the plan by destroying the facility where it's happening.]]
* BreatherEpisode: Episode 8 of Season 2, which focuses mostly on Shouko. At least until the very end of the episode...
* BrotherSisterIncest: Questionable as we don't know how DNA is selected, but seeing as [[spoiler: Nataru was taken from a lab called "Cephon" as a baby and their origins, it would appear that at least he and Birdy came from the same lab]].
* ButtMonkey: Tsuotmu, thanks to some of Birdy's antics.
* CameraAbuse: Early in the first season, Birdy kicks a piece of debris at the non-InUniverseCamera, which nevertheless tumbles backward and [[SnowyScreenofDeath cuts out with static]].
* TheCassandra: Muroto, a reporter who focuses solely on aliens. Almost everyone dismisses him as a conspiracy theorist.
* ChildhoodFriendRomance: Birdy and Nataru in ''Decode 02.'' They lived in the same city, but hadn't seen each other for years after a terrorist attack.
* ClingyJealousGirl: Shouko in ''Decode 02''.
* ClothingDamage: In ''Decode'', [[RobotGirl Ondine]]'s outfit is totally destroyed in a very short period of time. However, as a marionette, she has BarbieDollAnatomy.
* CombatStilettos: Justified in that Birdy uses her heels as kick-off propulsion devices/mini-rockets, though only the remake manga and ''Decode'' versions of Birdy has them.
** And they make such a cool sound, so who can blame the designers?
* CombatTentacles: Bacillus uses these in fighting Birdy.
* {{Crossdresser}}: Birdy (in the OVA) would sometimes shift into her form, but still wear Tsutomu's clothes.
** She does it a few times in the remade manga, too, despite being bigger than him.
*** She also did the same thing in the original manga.
* ConspicuousCG: Some of the alien vehicles in ''Decode.'' Though it's far from jarring and does blend much better than other shows.
* CrouchingMoronHiddenBadass: Muroto. When [[spoiler:he runs into Tsutomu during the Ryunka's attack, he gives the kid a ride right up to the police barriers while every other citizen is (understandably) getting the hell ''away''. Then he provides a very effective distraction so that Tsutomu can get to Sayaka]].
--> "Let's see... [[PreAsskickingOneLiner it's been about two weeks since I've been arrested for obstruction]]." [[spoiler:(proceeds to shoulder-charge several cops)]]
* DarkAndTroubledPast[=/=]HarmfulToMinors: Birdy's past, [[spoiler: especially regarding the death/destruction of a woman named Violin who was killed trying to protect Birdy when she was little. While not much was not revealed in the OVA, in the ''Decode'' series, Violin was revealed to be a RobotMaid who raised Birdy]].
* DatingCatwoman: In the second season of ''Decode'', Birdy meets up with Nataru, an old friend of hers at the same time as she's assigned to track down some escaped criminals involved in the events of the first season and over the course of the second season, develops feelings for him. At the same time, someone's been killing the escapees. [[spoiler: Nataru's the one killing off the escapees and fights Birdy when she saves one of the last remaining ones.]]
* DeadlyNosebleed: Nataru sports one when weakened by his time jumping capability.
* DemotedToExtra: Natsumi. In the OVA series, she's Tsutomu's classmate/LoveInterest, and has a fair amount of screentime. In Decode, however, she's no longer Tsutomu's crush (replaced by Sayaka) and only seen briefly in two or three episodes.
* DoesThisRemindYouOfAnything: The basic premise is remarkably similar to a long-running arc in {{Marvel}}'s [[CaptainMarVell Captain Marvel]] series, where an ordinary guy must share his body with a powerful superhero who has his own identity and motivations, right down to the two being able to talk to each other.
* TheDragon: Gomez. In the manga, there are also the four elemental robots -- Undine, Salamander, Sylph, and Gnome.
** Or maybe not Gomez. At the end of the OVA, [[spoiler: he says he might even take down Revi himself if he deems her just a terrorist]]. His role is also muddled in the remade manga, since he [[spoiler: takes in Chigira after he's turned into a beastman and helps him learn to control it. He also develops a more-or-less professional relationship with Birdy, who is willing to do so thanks to him taking care of Chigira]].
* DramaticChaseOpening: The OVA.
* DudeNotFunny: [[invoked]] Tsutomu sarcastically asks if Birdy's glad that Tuto isn't around so she can indulge in some creature comforts... [[spoiler:after Tuto was destroyed in the previous episode]]. She responds by making a fist and swapping back to his body long enough to sock him.
* EarthIsTheCenterOfTheUniverse: Completely averted. Earth is considered an insignificant backwater planet in the ''Decode'' universe.
* EyelidPullTaunt: In the original manga, Geega does this to mock Birdy after she accidentally kills Tsutomu.
** Hayamiya does it in ''Decode''.
* EyeScream: [[spoiler:In ''Decode 02'', Nataru viciously stabs his fingers into one of Gatol's eyes.]]
* FirstLawOfGenderBending: Tsutomu gains his body back in the first season finale of ''Decode'' only for it to be destroyed again and he's forced back into Birdy.
** ShapeshifterModeLock: Temporarily. See the "Freaky Friday Flip/Man, I Feel Like A Woman" example.
*** A longer but still temporary mode lock also exists in the remake manga. During the time-jump after the first series, Birdy's consciousness is put to 'sleep' for a couple of years, which happens to let Tsutomu finish high school and start into college as a 'normal' boy.
* EvilMinions / WesternAnimation/{{Robots}} / MechaMooks
* FairCop: Birdy.
* {{Fanservice}}: Though more low-key and tasteful (especially ''Decode'', like all A-1 productions) when compared to other series, it does exist. Usually, [[MsFanservice Birdy]] is the subject.
** ToplessnessFromTheBack: Especially in the remake manga where in one scene [[http://mangafox.me/manga/birdy_the_mighty_ii/v06/c062/12.html a doctor lampshades this by touching her rump.]]
** BarbieDollAnatomy: Birdy in the first part of the OVA, somewhat justified in one case by OutOfClothesExperience. Subverted in the second part near in the end when the only view of her front is from the [[ShouldersupNudity shoulders up]]. Averted in the last two parts as she's not in a situation where she's nude.
** BathKick: Birdy does this in the first episode of the second season of ''Decode''.
** BetweenMyLegs: Gets used in the first episode of ''Decode''.
** DirtyHarriet: In one episode of ''Decode'', Birdy poses as a prostitute at a bar for a short while.
** FuroScene: One scene in the OVA and frequent use in ''Decode''. Birdy also loves baths in the manga, since it's much more relaxing than the adjustment tub on her ship.
** FullFrontalAssault: A heroic version. As opposed to the OVA, Birdy in the original manga did not don her uniform when Bacillus was outside of Tsutomu's house and confronted him in the nude.
** FunbagAirbag: When Geega threw Tsutomu at Birdy in the original manga, Tsuotmu ends up slamming into Birdy and his face end up slamming into her chest.
** ImpossiblyLowNeckline: Birdy's outfit sports this.
** LeotardOfPower: Birdy's work outfit. Male officers are also seen wearing the same thing, so it's apparently the Investigator uniform. (The technology level allows shielding, so the lack of coverage isn't a defensive concern.)
** SensualSpandex: Birdy's outfit.
** SexyBacklessOutfit: Birdy, especially in ''Decode''.
* FashionableAsymmetry: In the OVA, the boot of Birdy's right leg only comes up to her knee while the one on the left stops at her thigh.
* FirstEpisodeResurrection: Tsutomu, though depending on which version you watch, how far into the first episode he dies varies; in the OVA, he dies within the first few minutes while in ''Decode'', he dies after the episode is halfway through.
* FantasticRacism: In ''Decode'' and the remade manga, it's revealed that Altirrans, Birdy's species, were the target of racism among other species and treated like lower-class citizens, especially following a terrorist attack.
* TheFederation: Technically where Birdy hailed from is called a Federation. Subverted because of the fact that the the human-like Altirrans are more or less lower-class citizens and treated like crap and that the Federation has a program to use Altirran DNA to bioengineer SuperSoldier, [[spoiler: one of whom is Birdy herself]].
* {{Flashback}}
** FlashbackCut: [[spoiler: Violin's death in the OVA]]. Outside of the sixth and maybe seventh episodes, the teasers to the second season of ''Decode'' could also be considered this.
** WholeEpisodeFlashback: Two episodes in the second season of ''Decode'', showing Birdy's past. Also an entire volume of the remade manga.
* FourEyesZeroSoul: [[spoiler: Shyamalan]].
* FreakyFridayFlip[=/=]ManIFeelLikeAWoman: Happens in ''Decode'' -- [[spoiler:After obtaining injuries during a battle in episode five of the second season, Birdy passes out and Tsutomu awakens to find himself in Birdy's form and [[ShapeshifterModeLock unable to change back]]. This lasts through Episodes 6 and 7, which are the aforementioned WholeEpisodeFlashback examples, where he journeys into her memories and is resolved by the end of episode seven when he finds Birdy and things are returned to normal]]. The manga is more appropriate to ManIFeelLikeAWoman since [[spoiler:the first thing Tsutomu does when he realizes he's in Birdy's body is to grab his chest and groin in disbelief. His time before journeying into Birdy's past is shorter, and he at least again checks his groin after returning to his body just to be sure that everything was proper again]].
* GambitPileup: Deconstructed. In the beginning, there are several factions involved, along with multiple wild cards, a chessmaster, and neutral but interested parties. And that's just the first season, on the alien side. However, instead of there being any JustAsPlanned and IKnowYouKnowIKnow, bad intelligence and lack of information reigns supreme, with things devolving into a chaotic world where the law of unintended consequences dictates the outcomes of events more than anything else. No one really knows what the hell is going on, except maybe the viewer, and even they, who see a lot more than any given character must think quite a bit and infer a lot to figure out what really happened and why.
* GeneticEngineeringIsTheNewNuke: [[spoiler: In ''Decode'', it's revealed that Birdy and Nataru were the result of a program to bred super-soldiers via bioengineering]].
* GeniusBruiser: Skeletso, who taught Birdy how to fight, greets his subordinates with a flying attack, and runs a successful undercover operation.
** Birdy herself counts too. Despite being raised solely for combat, she delves into pretty advanced philosophy of life and moral philosophy.
* GoneHorriblyRight: A tragic case for a benevolent scientist working on marionettes. [[spoiler:When she asked it to give her a hug, it crushed her to death--then it escaped and began killing women who looked like the scientist, searching for its "mama."]]
* GoryDiscretionShot: To varying degrees. [[spoiler: Faroid]], in a way, and [[spoiler: his sister later]]. Otherwise, ''Decode 02'' doesn't usually bother with it.
* HairTropes
** AnimeHair: Birdy in the original manga and OVA tended to have spiky bangs.
** FieryRedhead: Well, Birdy's got pink hair and it's only one of [[MulticoloredHair two]] (the other being white), but close enough. Similarly, Capella Titis has mostly pink hair with large sections of white.
** GodivaHair: Remake manga and ''Decode'' Birdy. The original manga and OVA versions, not so much.
** HairDecorations: In the original manga and OVA, Birdy sports a hairband with triangular clips around her ears. In the remake manga and ''Decode'', she sports a headset with two fin-like protrusions, each also around her ears.
** ImplausibleHairColor: Natsumi, a couple of Tsuotmu's other classmates, and a few other fall into this.
** MulticoloredHair: Birdy's hair is a combination of pink and white. Depending on the version, the placement of the coloring varies. It's white on the right and pink on the left in the original manga and OVA; pink for the bangs, but otherwise white in the remake manga; and pink for the bangs and bottom of her mane but otherwise white in ''Decode''.
** PowerDyesYourHair: [[spoiler: Nataru when he activates his powers]]
** TomboyishSidetails: Birdy sports these.
* HalfTheManHeUsedToBe: How Birdy actualy kills Tsutomu in ''Decode.''
* HandOrObjectUnderwear: In the OVA, Tsutomu used his hands to cover himself up to run back to the bathroom to grab the clothes while his family was standing around.
* HeroicRROD: In ''Decode 02'' [[spoiler: the result of Nataru overusing his powers]].
* HeroicSacrifice: In the remake manga, [[spoiler: Tuto dies while trying to keep Tsutomu alive]] and in ''Decode'', [[spoiler: Tsutomu (who's just regained his body) takes the Ryunka into his own body so that Birdy can destroy it without killing Sayaka. Fortunately, he's able to share her body again]].
* HoistByHisOwnPetard: Hikawa in the OVA and Shyamalan in the first season of ''Decode''. Hikawa was messing with a serum that was supposed to create SuperSoldiers that had a history of mutating people into monsters and used himself as a subject, while Shyamalan tried to control the Ryunka, a weapon capable of killing everything on the planet. [[spoiler: Hikawa ended up being turned into a monster in the last episode of the OVA and Shyamalan, [[TooDumbToLive being literally in the same room with a not fully-mature Ryunka while messing with it in his efforts to control it]] was one of the first to die in the final episodes of the first season of ''Deocde''. In the remade manga, Hikawa also uses himself as a test subject, but ends up doing ''too'' good against Birdy causing her to go berserk and rip him apart before Tsutomu could calm her down.]]
* HollywoodSilencer: The pistol at the end of episode 8 in ''Decode: 02''.
* HoodHopping: During a highway chase scene, Birdy and an Arkazoid [[http://www.youtube.com/watch?v=ZBd2yg5ayLQ#t=2m56s leap across moving vehicles]] in rush hour traffic.
* HotterAndSexier: Birdy's uniform in the remake manga and ''Decode'' tends to cover less than the uniforms in the original manga and OVA.
* HumongousMecha: An episode of the ''Decode'' series has a giant mecha that resembles its pilot.
* HumanAlien: Birdy, Gomez, Christella Revi in the OVA. '''All''' Altirrans in ''Decode'', and for once it is deconstructed. The FantasticRacism applied to the human-like Altirrans is extended to Terrans themselves due to the resemblance. In this sense, it is contextually inverted, as Terrans are thought to be the look alike, not Altirrans. Further played with when it is revealed that Earth functions as a kind of refugee camp for Altirrans wishing to escape persecution, not to mention the usual hideout used by aliens-in-disguise.
* IHaveManyNames: In a meta sense, the series of robots that [[spoiler: Violin]] and the MechaMooks Birdy deal with. Depending on the incarnation, they're either called Arkazoids (original manga and OVA), Dolls (remake manga), or Marionettes (''Decode'').
* IdolSinger: Birdy's alter ego of Shion Arita is one.
* IllGirl: Sayaka, before a horrific car crash [[spoiler:and being infected with the Ryunka]].
* InSeriesNickname: Berserker Killer Birdy.
* JourneyToTheCenterOfTheMind: The FreakyFriday / ManIFeelLikeAWoman and WholeEpisodeFlashback examples, the former setting it off and justifying the latter, where [[spoiler: Tsutomu had to rescue Birdy after getting stuck in her form and how he learned of her past. In the manga, this knowledge becomes very handy when some of Birdy's old classmates show up on Earth]].
* KillSat: An episode of ''Decode'' has a Kill Sat intended to stop the main threat of the first season. As per usual with the trope, it failed.
* KickTheDog: Reversed in episode 6 of season 2 in the memory sequence with Nataru.
* LawyerFriendlyCameo: [[KeroroGunsou Giroro]] makes one in episode 5 of ''Decode''.
* LightningBruiser: Birdy, and the [[SpellMyNameWithAnS Undine/Ondine]] even more so.
* MadScientist
* MagicPants: The OVA played around with this. Initially Tsutomu's outfit did not change when Tsutomu changed into Birdy, leading to a girl in boy's clothing kicking monsters around. Later she incorporated her leotard-like uniform into the matrix so she'd be in her clothes, not his, after a transformation.
* MamaBear: [[spoiler: Violin, prior to her death in ''Decode'', took out several robots while she was trying to find and protect Birdy.]]
* TheMasquerade: ZigZagged to hell and back in ''Decode''. While the population at large is generally unaware of the aliens' presence, and many people don't believe in aliens, one may suspect that Masakubo's obsession with aliens and UFOs is more than crazy conspiracy theory paranoia. The non-humanoid aliens usually have some kind of disguise to make themselves look human and blend in, but many aliens have revealed themselves, making business deals with human companies and (possibly) governments. Even Birdy has the Shion Arita identity, but [[spoiler: she revealed herself to Muroto, though he may or may not have believed her]]. No cover up efforts are made at all when [[spoiler: the Ryunka demolishes the countryside]], and everyone knows something weird happened when [[spoiler: the Ryunka completely trashed the Roppongi area]]. The government must have known something was up when [[spoiler: the aliens assaulted a military base and stole a nuclear bomb]]. But on the other side, some aliens living on earth might not even know they are alien, because they either were born there or moved when very small and their parents never told them. [[spoiler:For example, in ''Decode'', it is revealed that Chikira is an Altan, though he may or may not know this.]]
* MindHug: [[spoiler:Tsutomu to Nataru in the last episode of ''Decode02''.]]
* MistakenForGay: In ''Decode'', Tsutomu's friends first meet Tuto when he brings Tsutomu his gym clothes and demonstrates a [[NoSenseOfPersonalSpace notable disrespect for his personal space]]. They decide to support the two's relationship.
* MistakenForMurderer: In the second season of ''Decode'', several criminals escape, then one by one, each of their number is killed. The survivors assume wrongly that it's Birdy and that she was given orders to silence them for their involvement in the events of the first season.
* MoodWhiplash: ''Decode'' can get very dark at times -- [[AnimeThemeSong Let's go! Have a good time!]]
* MoralityPet: Tuto, a shapeshifting AI, who assigned as a partner to Birdy in the remake manga and ''Decode.'' While what don't see how Birdy reacted to what she did to Tsutomu in ''Decode'', in the remake manga she actually suggests covering it up until Tuto points out that he's recording and broadcasting what happened to her bosses and Birdy decided to help Tsutomu. While we don't know what happened in ''Decode'' between Birdy's reaching out to Tsutomu and their fusion, it should be pointed out that as Tuto doesn't exist in the original manga and OVA and hence Birdy in those was more willing to own up to her mistake without anyone telling her to do so.
* MundaneSolution: In the OVA, Tsutomu figures out that one of the aliens can be defeated with ordinary dish soap. In the remade manga, gasoline does the trick, though it's Birdy that realizes it [[spoiler: and is then scolded by Tsutomu for destroying a car to dump gas on herself and the attacking alien]].
* MyGodWhatHaveIDone: Pretty much sums up Birdy's reaction to fatally wounding Tsutomu.
* NakedPeopleAreFunny: Tsutomu's dad catching Birdy in the bath (only Birdy was nude in the original manga, but both people were in the OVA and remake manga), Tsutomu running through the house naked (partly due to the aforementioned event and he was in a hurry to grab a cleaning agent to help Birdy stop Bacillus) in the original manga and OVA, and in the remake manga, Birdy using Tsutomu as a [[PeoplePuppets Person Puppet]] during that version of the said event as well, causing Tsuotmu's family and Hayamiya to wonder what's going on.
* NamesToRunAwayFromReallyFast: DoubleSubverted with Birdy's nickname, Berserker Killer Birdy. Turns out it doesn't mean TheBerserker, it refers to the fact that she killed robots called Berserkers. The second subversion comes in when we find out these things give ''armies'' a run for their money.
* NotInThisForYourRevolution: [[SubvertedTrope Subverted]]. Birdy's mission in the original manga, OVA, and the remake manga is to arrest Christella Revi, but as Revi had to do with an attack that [[spoiler: killed Violin]], Birdy has a personal axe to grind with her. While this doesn't apply to Revi in ''Decode'' (Birdy doesn't know Revi's on Earth and her mission's somewhat different), in the second season, she also has a personal grudge against one of the escaped aliens she's supposed to recapture for similar reasons.
* ObfuscatingStupidity: Birdy uses this in both seasons of ''Decode'' when in her alter ego of Shion Arita.
* OlderThanTheyLook: Hikawa in the OVA looks to be in his twenties, but [[spoiler: he's really a scientist who was active in World War II, though this was more or less using himself as a test subject after meeting Revi as a flashback to before the events of the OVA and his body after his death does show him at his true age]].
* OffModel: ''Decode 02'', Episodes 7 and 12, due to serious budget problems.
* {{Ojou}}: Sayaka in ''Decode''. Also an IllGirl and [[spoiler:PersonOfMassDestruction]].
* OrdinaryHighSchoolStudent: Tsutomu, and even more-so his friends.
* ParentalAbandonment: Tsutomu's family in ''Decode'', as mentioned in BatmanInMyBasement, aren't present. His parents move to another city for his dad's job, but leave him in the house so he can stay in the same school.
* PeoplePuppets: Birdy at times tends to take control of Tsutomu's form, much to the latter's annoyance and anger. In the remade manga, she tries to use his body to fight much to his relief, as [[spoiler: he had accepted that the only way to save his friends from harm was for her to transform and fight off a monster. She ends up not being able to fight well in his form, but it all turns out okay in the end]].
* PleasePutSomeClothesOn: In both the original manga and the OVA, Tsutomu asks Birdy to do this when she goes out to confront Bacillus. In the OVA, she complies, but in the original manga, she ignores the requests and confronts Bacillus in the nude.
* PossessionBurnout: Bachilus's possession causes the body to decay.
* PosthumousCharacter: [[spoiler: Violin]]
* PowerGlows: In ''Decode'', the Ryunka manifests as a blue glow emanating from its host. (Well, that and horrible destruction.)
* PunchCatch: In the OVA, when Birdy and Hikawa finally fight, Hikawa does this to the first punch Birdy takes at him.
* RecurringExtra: In ''Decode'', the two yakuzas whose car keeps getting damaged by Birdy.
* RedOniBlueOni: Hayamiya ([[{{Tomboy}} tomboyish]] FieryRedhead GenkiGirl) and Nakasugi (blue-haired {{ojou}})
* TheRevolutionWillNotBeCivilized[=/=]WellIntentionedExtremist[=/=]YourTerroristsAreOurFreedomFighters: In the flashback we see in the second season of ''Decode'', a lot of Revi's actions are an attempt to force the Federation to improve the lot of Altirrans so they aren't treated with racism and like lower class citizens anymore. A lot of her actions have included terrorist attacks on key government building, allying herself with members of the Federation's enemies, and [[spoiler: trying to obtain a DoomsdayDevice]] In the manga, the story is a little bit different. Revi is recognized as a genius, and quickly climbs to a high rank in the government science branch despite her race. Her terrorist attack on the central government is inexplicable, and followed by several more destructive bombings before disappearing to Earth.
** [[spoiler: Nataru]] is also starts out a WellIntentionedExtremist, taking out the group most of the group of escaped aliens for the role in what happened in Season 1 of ''Decode''. He slips into MoralEventHorizon when he kills two of them who disguise themselves as childern, one of them even deciding to leave the others in protest of what they're doing.
* RoaringRampageOfRevenge: [[spoiler:Nataru]] in ''Decode 02''. Once he finds out the people responsible for the death of his friend, he makes sure they die and/or suffer horribly. Even Birdy has trouble against him initially when she tries to stop him.
* RobotMaid
* RobotGirl: Ondine/Undine.
* RoofHopping: How Birdy travels to catch criminals.
* SamusIsAGirl: Not a strict use of the trope as Revi isn't an ActionGirl, but in the remake manga and ''Decode'' no one, not even Birdy, outside a few people know that she is a woman. Averted in the original manga and OVA where it's pretty well-known what gender Revi is. In the remade manga, [[spoiler: Tsutomu and his family even end up staying at Revi's house for a little without him or Birdy realizing it]].
* ScaryShinyGlasses: Satayjit Shyamalan does this in spades.
* SecretIdentity[=/=]WigDressAccent[=/=]ClarkKenting: In ''Decode'', prior to being merged with Tsutomu and even afterwards, Birdy assumed the name "Shion Arita". This didn't stop a photographer, Tsutomu himself, or someone from her past from recognizing her. Averted in the OVA when Birdy's normal hair is visible and doesn't bother acting too differently.
* SentOffToWorkForRelatives: After everyone in her family/household is dead, to causes both related and unrelated to the plot, Sayaka is sent to work on a farm with relatives.
* ShapeshiftingExcludesClothing: Happens in ''Decode'', where the world-destroying parasitic weapon, Ryunka, spreads to the Greater Tokyo Area, petrifying any person into a glass-like substance that [[LiterallyShatteredLives shatters]] into dust, leaving behind nothing but piles of clothing. The death of Nataru's (one of Birdy's childhood friends and fellow Altarian) buddies from the Ryunka's destruction is what prompts him to go on a {{Roaring Rampage of Revenge}} in the second season against the criminals responsible for releasing it.
* [[HeWhoMustNotBeSeen She Who Must Not Be Seen]][=/=]TheVoice/[[ManBehindTheMan Woman Behind the Man]]: Revi in ''Decode'' for the most part. The viewer does get to actually see her during the last scene of the first season of ''Decode'', though.
* ShockAndAwe: In the OVA, Birdy can electrocute people by grabbing them and unleashing an electric shock into them. This is how she accidently kills Tsutomu and [[spoiler: after absorbing power from an electricity plyon, defeats a mad scientist after he mutated as a result of his own serum]].
* ShootingSuperman: As seen once in the OVA and twice in ''Decode'', shooting Birdy with a gun isn't really effective to take her down, though she will twitch or get knocked down upon the bullets' impacts and, as she expressed once in ''Decode,'' the impacts do hurt. In the manga, this is explained by a biological shield, but it's not invincible and with proper attacks [[spoiler:can be pierced even by a knife]].
* SlasherSmile: [[spoiler: Nataru]] sports these as he kills the escaped aliens.
* TheSocialDarwinist: Shyamalan ([[Creator/MNightShyamalan no, not that one]]) in ''Decode''. He believes that the Ryunka will let him choose the worthiest of humans and destroy the rest. [[spoiler:Boy, was he wrong.]]
* SoleSurvivor: [[spoiler:Shyamalan]] was the only person in a gathering of 4,000 to survive a terrorist bombing. This combined with his reputation as a ChildProdigy was his StartOfDarkness.
* SpacePolice: Birdy is a space cop.
* SpeciesSurname: Regardless of spelling (see below), names in Birdy's society work differently than in ours. The first name is basically the same as ours, being an identifier unique to the individual. Birdy in Birdy's case of course. The last name is the name of one's species; Birdy's last name is Altirra because she is an Altan. The middle name is a bit muddier, as Birdy's is the only one explicitly given: Cephon. It is the name of the [[spoiler: place/spawning device where she was created. It can be inferred that other artificial life forms' middle name works like this, but it is unknown whether 'natural' people's middle names come from some equivalent, or if they even have them.]]
* SpellMyNameWithAnS: The subtitles of the OVA prefer to romanize the last part of Birdy's name as "Altirra," though fans have also used "Altera." The English dub switched "Cephon" and "Altirra" around, resulting in "Birdy Altirra Cephon". Then there's "Altaria" ([[Franchise/{{Pokemon}} Uh...]]), used by Funimation on Website/{{Youtube}} for ''Decode''. The DVD release was contradictory, as the subtitles used "Altira", but the credits used "Altera". Though technically, "Altirra/Altera/Altaria" is only used to identify where Birdy's from and her species and really isn't offically part of her name. also, in an in-universe example, on earth in the modeling business, Birdy goes by the name 'Shion Arita', which seems to be a corruption of 'Cephon Altirra'.
** Revi's android daughter name is either spelt Ondine or Undine.
** Then there's [[spoiler: Violeen/Violene/Violin]].
* SpoiledSweet: Sayaka.
* StableTimeLoop: [[spoiler: Two of the times Nataru uses his powers to go back in time, he caused two of these. The first, when disposing of a bomb that Moss used to try to kill him resulted in him meeting Shoko's brother and the other revealed him as the mystery man who saved a young Birdy during the Central Tower attack.]]
* SuperCop: Birdy herself.
* {{Superhero}}
* SuperSoldier: One of the villains in the OVA tries to create these via a serum. According to ''Decode'', [[spoiler: Birdy herself is one, created through being a result of [[GeneticEngineeringIsTheNewNuke a bioengineering program]] to created [[SpaceMarines soldiers]] and [[SpacePolice police officers]].]]
* SweatDrop: Birdy does this upon finding a bomb just as it's about to go off in the OVA.
* TerrorHero: Birdy is one of the rare non anti-heroic examples. She is known as "Berserker Killer Birdy" (see the Berserker entry on this page for an explanation of that), and also strikes fear into the hearts of her opponents because she is an Ixioran. This trope manifests especially when [[spoiler: The fugitives start being brutally murdered, and the first conclusion they jump to is that Birdy is responsible.]]
* TitleDrop: Birdy does this in a made-up speech in the original manga.
* TokyoIsTheCenterOfTheUniverse: Natch, though in season 2 of ''Decode'' [[spoiler:out of all of Earth's cities Season 2's villains could have escaped to, it somehow just HAD to be Tokyo. While the city is indeed an apparent favorite for the series's aliens, the group in question were partly responsible for a narrowly avoided Class X annihilation event who's epicenter was Toyko, which led to the firing of a KillSat on the city, the resulting ruins of said firing being a major set piece throughout the season.]]
** Justified in season 2, where [[spoiler:one of the escapees explicitly says he wanted to go to the place where the Ryunka was used]].
** An earlier episode implies that the amount of alien activity in Tokyo is actually not unusual for a city its size. Presumably every comparable city on Earth has lots of disguised aliens running around, too.
* TrainingFromHell: [[spoiler: What Birdy goes through as a kid in preperation to be a Federation officer.]]
* TwelveEpisodeAnime: The ''Decode'' series. Literally in the case of the second season.
* TwoBeingsOneBody[=/=]FusionDance[=/=]GenderBender[=/=]SharingABody[=/=]TheyFightCrime: Series Premise.
* TykeBomb: In ''Decode'', [[spoiler: Birdy, as part of being a super soldier, was trained as a little kid how to fight in preparation for her being becoming an investigator]]. In the manga, [[spoiler: she receives similar harsh training since she's an Ixiora.]]
* UnexplainedRecovery: Invoked with Sayaka Nagasuki after a car wreck. She's not expected to survive, but the next day she's fully recovered and cured of her previous IllGirl status. Her grandfather accepts it as a miracle but their maid is deeply concerned. [[spoiler:For very good reason, as the "miracle" was caused by an ancient biological super-weapon.]]
* UnflinchingWalk: Birdy does this after detonating Bacillus in episode 3 of Decode.
* UnstoppableRage: [[spoiler: Birdy's reaction to Violin's death and the realization of her being a robot in ''Decode'' involves completely and violently dismantling the robot that killed her while denying Violin was a robot. Birdy only calmed down after passing out]]. In the manga, [[spoiler: she reacts the same way to Violin's death, going berserk and beating the robot to bits with its own claw. Later, she goes berserk on Hikawa after he learns how to penetrate her shield and slices her up some. In the currently-running sequel, she again goes berserk after finding the photo of a small girl (whom she had just recently met and had to protect) in the files of another of Revi's research centers. Her (and Tsutomu's) rage leaves the entire building in ruins]].
* VagueAge: Birdy's age isn't specified in either the OVA or ''Decode''. In the OVA, she's clearly older than Tsutomu, but according to Tsutomu, she's too young to drink alcohol, which means she could be somewhere in the 17-19 age range. Doing the math in the ''Decode'' version, based on references to her past in the second season offer that she's probably at least 24 there.
* VerbalTic: In the Japanese version of ''Decode'', Birdy as Shion Arita tends to accent the "u" sounds in words that have them and add "de arudesu" to a lot of sentences.
* VitriolicBestBuds: Tsutomu and Hayamiya have this dynamic.
* VoiceOfTheLegion: During episodes 5 and 6 of Decode 02, [[spoiler: while Tsutomu is [[ShapeshifterModeLock stuck]] in Birdy's form when he's on her ship, he was protrayed as speaking with both his and Birdy's voice at the same time]].
* VoluntaryShapeshifting: Tsutomu and Birdy generally switch willingly, but there are still exceptions where Birdy takes over (or reverts back to) Tsutomu without warning.
* VSign: In the first three parts of the four part OVA series, the credits would end with an image of Birdy flashing this.
* WaterSourceTampering: This was Seichiro Hikawa's plan for the people of Tokyo, to turn them into "retro soldiers" by tainting the city's water supply with serum.
* WeHardlyKnewYe: In the remake manga and ''Decode'' series, Tuto. [[spoiler: In the remake manga, he sacrifices himself to keep Tsutomu alive; and in the third episode of the first season of ''Decode'', he's blown up and damaged beyond anyone's ability to repair him as he was. He's later rebult into a computer, but is not the same as he was prior to his death. In the manga, many of his features are rebuilt into Tsutomu's cell phone which was broken with his body, making it a parallel to himself and Birdy.]]
* WhatMeasureIsANonHuman: Both averted and played straight. Averted in that the various alien races pretty much agree they're equals (even though you can still spot a bit of FantasticRacism here and there), played straight in that those very same alien races treat [[ArtificialHuman Dolls]] as little more than a commodity, despite them being clearly sentient.
* WhatTheHellHero: In the remake manga, Birdy actually considered trying to cover-up what happened to Tsutomu before MoralityPet Tuto pointed out that he was recording what happened and hence it was impossible, so Birdy decides to help Tsutomu after all. How serious she was is questionable, but she's reprimanded by her superiors none-the-less.
* TheWoobie: InUniverse, Sayaka is this to her classmates due to her sweet personality, orphanhood, and chronic illness.
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