Tsutomu Senkawa was an ordinary kid living in Tokyo. Birdy Cephon Altirra/Altera/Altaria was a beautiful Space Cop 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 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 Madhouse with direction by Yoshiaki Kawajiri of Ninja Scroll 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 The Vision of Escaflowne 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 here!
Aliens Speaking English / Translation Convention: 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.
Also, the OVA and original manga follow a very similar continuity, while the remake manga follows a similar but different continuity.
Art Shift: 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.
Attack Hello: 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.
Bad Dreams: Shyamalan in Decode, involving fire and explosions. Not that they get him many sympathy points, what with everything he does while awake.
Bathtub Bonding: As noted above, Tsuotmu's dad tried to do this with his son, but ended up discovering Birdy.
The Berserker: 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.
Berserker Tears: Birdy's crying these when she's trashing the robot that killed Violin.
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, Birdy and Nataru are artificial bioengineered humanoid weapons, and the Ryunka is another, probably artificial, biological weapon.
Bitch in Sheep's Clothing: 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.
Bittersweet Ending: The first season of Decodeends with Tsutomu's girlfriend leaving after being separated from the Ryunka, a Doomsday Device, 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...
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. In the OVA, he bonds himself to several dogs at once before before getting repelled by dish soap, then bonds himself to some Mecha-Mooks 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. 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. 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.
Breather Episode: Episode 8 of Season 2, which focuses mostly on Shouko. At least until the very end of the episode...
Brother-Sister Incest: Questionable as we don't know how DNA is selected, but seeing as 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.
Butt Monkey: Tsuotmu, thanks to some of Birdy's antics.
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.
Conspicuous CG: Some of the alien vehicles in Decode. Though it's far from jarring and does blend much better than other shows.
Crouching Moron, Hidden Badass: Muroto. When 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.
Dark and Troubled Past/Harmful to Minors: Birdy's past, 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 Robot Maid who raised Birdy.
Dating Catwoman: 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. Nataru's the one killing off the escapees and fights Birdy when she saves one of the last remaining ones.
Deadly Nosebleed: Nataru sports one when weakened by his time jumping capability.
Demoted to Extra: Natsumi. In the OVA series, she's Tsutomu's classmate/Love Interest, 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.
Does This Remind You of Anything?: The basic premise is remarkably similar to a long-running arc in Marvel's 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.
The Dragon: 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, 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 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.
Dude, Not Funny!: invoked Tsutomu sarcastically asks if Birdy's glad that Tuto isn't around so she can indulge in some creature comforts... 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.
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.
Barbie Doll Anatomy: Birdy in the first part of the OVA, somewhat justified in one case by Out-of-Clothes Experience. Subverted in the second part near in the end when the only view of her front is from the shoulders up. Averted in the last two parts as she's not in a situation where she's nude.
Bath Kick: Birdy does this in the first episode of the second season of Decode.
Leotard of Power: 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.)
Fashionable Asymmetry: 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.
First Episode Resurrection: 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.
Fantastic Racism: 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.
The Federation: 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 Super Soldier, one of whom is Birdy herself.
"Freaky Friday" Flip/Man, I Feel Like a Woman : Happens in Decode — 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 unable to change back. This lasts through Episodes 6 and 7, which are the aforementioned Whole Episode Flashback 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 Man, I Feel Like a Woman since 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.
Gambit Pileup: 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 Just as Planned and I Know You Know I Know, 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.
Genius Bruiser: 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.
Gone Horribly Right: A tragic case for a benevolent scientist working on marionettes. 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."
Gory Discretion Shot: To varying degrees. Faroid, in a way, and his sister later. Otherwise, Decode 02 doesn't usually bother with it.
Anime Hair: Birdy in the original manga and OVA tended to have spiky bangs.
Fiery Redhead: Well, Birdy's got pink hair and it's only one of two (the other being white), but close enough. Similarly, Capella Titis has mostly pink hair with large sections of white.
Godiva Hair: Remake manga and Decode Birdy. The original manga and OVA versions, not so much.
Hair Decorations: 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.
Multicolored Hair: 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.
Hand or Object Underwear: 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.
Heroic RROD: In Decode 02 the result of Nataru overusing his powers.
Heroic Sacrifice: In the remake manga, Tuto dies while trying to keep Tsutomu alive and in Decode, 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.
Hoist by His Own Petard: Hikawa in the OVA and Shyamalan in the first season of Decode. Hikawa was messing with a serum that was supposed to create Super Soldiers 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. Hikawa ended up being turned into a monster in the last episode of the OVA and Shyamalan, 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.
Hotter and Sexier: Birdy's uniform in the remake manga and Decode tends to cover less than the uniforms in the original manga and OVA.
Humongous Mecha: An episode of the Decode series has a giant mecha that resembles its pilot.
Human Alien: Birdy, Gomez, Christella Revi in the OVA. All Altirrans in Decode, and for once it is deconstructed. The Fantastic Racism 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.
I Have Many Names: In a meta sense, the series of robots that Violin and the Mecha-Mooks Birdy deal with. Depending on the incarnation, they're either called Arkazoids (original manga and OVA), Dolls (remake manga), or Marionettes (Decode).
Magic Pants: 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.
Mama Bear: Violin, prior to her death in Decode, took out several robots while she was trying to find and protect Birdy.
The Masquerade: Zig-Zagged 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 UF Os 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 she revealed herself to Muroto, though he may or may not have believed her. No cover up efforts are made at all when the Ryunka demolishes the countryside, and everyone knows something weird happened when the Ryunka completely trashed the Roppongi area. The government must have known something was up when 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. For example, in Decode, it is revealed that Chikira is an Altan, though he may or may not know this.
Mind Hug: Tsutomu to Nataru in the last episode of Decode02.
Mistaken for Murderer: 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.
Morality Pet: 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.
Mundane Solution: 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 and is then scolded by Tsutomu for destroying a car to dump gas on herself and the attacking alien.
Naked People Are Funny: 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 Person Puppet during that version of the said event as well, causing Tsuotmu's family and Hayamiya to wonder what's going on.
Not in This for Your Revolution: 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 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.
Older than They Look: Hikawa in the OVA looks to be in his twenties, but 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.
Off Model: Decode 02, Episodes 7 and 12, due to serious budget problems.
Parental Abandonment: Tsutomu's family in Decode, as mentioned in Batman in My Basement, 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.
People Puppets: 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 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.
Please Put Some Clothes On: 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.
The Revolution Will Not Be Civilized/Well-Intentioned Extremist/Your Terrorists Are Our Freedom Fighters: 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 trying to obtain a Doomsday Device 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.
Nataru is also starts out a Well-Intentioned Extremist, 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 Moral Event Horizon 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.
Roaring Rampage of Revenge: 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.
Samus Is a Girl: Not a strict use of the trope as Revi isn't an Action Girl, 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, Tsutomu and his family even end up staying at Revi's house for a little without him or Birdy realizing it.
Secret Identity/Wig, Dress, Accent/Clark Kenting: 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.
Sent Off To Work For Relatives: 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.
Shapeshifting Excludes Clothing: 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 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.
Shock and Awe: 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 after absorbing power from an electricity plyon, defeats a mad scientist after he mutated as a result of his own serum.
Shooting Superman: 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 can be pierced even by a knife.
Slasher Smile: Nataru sports these as he kills the escaped aliens.
Species Surname: 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 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.
Spell My Name with an S: 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" (Uh...), used by Funimation on 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.
Stable Time Loop: 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.
Sweat Drop: Birdy does this upon finding a bomb just as it's about to go off in the OVA.
Terror Hero: 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 The fugitives start being brutally murdered, and the first conclusion they jump to is that Birdy is responsible.
Title Drop: Birdy does this in a made-up speech in the original manga.
Tokyo Is the Center of the Universe: Natch, though in season 2 of Decodeout 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 Kill Sat on the city, the resulting ruins of said firing being a major set piece throughout the season.
Justified in season 2, where 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.
Training from Hell: What Birdy goes through as a kid in preperation to be a Federation officer.
Tyke Bomb: In Decode, 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, she receives similar harsh training since she's an Ixiora.
Unexplained Recovery: 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 Ill Girl status. Her grandfather accepts it as a miracle but their maid is deeply concerned. For very good reason, as the "miracle" was caused by an ancient biological super-weapon.
Unflinching Walk: Birdy does this after detonating Bacillus in episode 3 of Decode.
Unstoppable Rage: 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, 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.
Vague Age: 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.
Verbal Tic: 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.
Voice of the Legion: During episodes 5 and 6 of Decode 02, while Tsutomu is 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.
Voluntary Shapeshifting: Tsutomu and Birdy generally switch willingly, but there are still exceptions where Birdy takes over (or reverts back to) Tsutomu without warning.
V Sign: In the first three parts of the four part OVA series, the credits would end with an image of Birdy flashing this.
Water Source Tampering: 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.
We Hardly Knew Ye: In the remake manga and Decode series, Tuto. 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.
What Measure Is a Non-Human?: 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 Fantastic Racism here and there), played straight in that those very same alien races treat Dolls as little more than a commodity, despite them being clearly sentient.
What the Hell, Hero?: In the remake manga, Birdy actually considered trying to cover-up what happened to Tsutomu before Morality Pet 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.
The Woobie: In-Universe, Sayaka is this to her classmates due to her sweet personality, orphanhood, and chronic illness.