* BetterOnDVD: DVD release partially cleaned up animation for second season of ''Decode'', or at least in certain scenes.
* CompleteMonster:
** {{OVA}}: [[EvilutionaryBiologist Seichiro Hikawa]] is an amoral biologist seeking to forcibly evolve the human race solely so his genius can be recognized. Originally an UsefulNotes/ImperialJapan war criminal responsible for heinous experiments, Hikawa faded into exile following UsefulNotes/WorldWarII. When the enigmatic alien terrorist [[WellIntentionedExtremist Christella Revi]] sought his expertise for her own ends, Hikawa saw this as an opportunity to revive his failed dreams. Through Revi's resources, Hikawa enacts a plot to [[WaterSourceTampering contaminate Japan's water supply]] with an experimental serum to mutate its citizens into psychic metahumans enslaved to his will. When confronted with the fact his plan will undoubtedly fail and kill everyone in Japan instead, Hikawa in a rage unleashes the serum into the sewers anyways.
** ''Birdy the Mighty II''[=/=]''Evolution'':
*** [[BodySnatcher Bacillus]], a [[AliensAreBastards parasitic alien]] who is originally a tenuous ally of Christella Revi, would prove to be far worse than he seemed. Investigating Birdy Cephon following the death of fellow smuggler Geega, Bacillus develops an obsession with taking her body for himself. After being repelled in a battle, Bacillus is consumed by rage and [[NoHonorAmongThieves abandons Revi for his own self-serving interests]]. [[CopKiller Murdering a police detective]] to assume a cover, Bacillus quickly forgoes any subtlety and massacres many policemen before instigating a [[AxesAtSchool high school shooting]] to draw Birdy out into the open.
*** [[MadScientist Shogo, ultimately revealed to be Seichiro, Hikawa]] may be human but proves to be the worst of his kind and among the most wicked adversaries Birdy Cephon ever faced. An enigmatic UsefulNotes/WorldWarII biologist whose youth was restored by Christella Revi's aid, Hikawa, under the guise of being a grandson to himself, plots to restore UsefulNotes/ImperialJapan and TakeOverTheWorld. Financed by a multi-governmental conspiracy to produce SuperSoldiers, Hikawa happily abuses his supposed invulnerability to maximize suffering upon anyone unfortunate enough to fall into his clutches, often only for his amusement. No one is safe from Hikawa's cruelty, not even children or whole families, which he abducts and slaughters in droves to the disgust of everyone around him. A narcissistic madman with delusions of grandeur, in the end Hikawa accomplishes nothing but spreading suffering and turning all his allies against him.
*** [[SinisterMinister Bishop Mace]] proves that even in the Federation's sinister department of worship. a whole new low can be reached. An insecure man who [[ItsAllAboutMe prizes his given authority above all else]], Mace was assigned captain of the assassination squad dispatched to kill Christella Revi after Birdy Cephon reported her location to her superiors. His subordinate Nechla Geeze, worried over Mace's general incompetence and bloodlust, misleads him to kill or detain Revi personally before his arrival. After failing in her mission and being captured, Mace, incensed by her subverting his authority, declares Nechla's lack of response as proof of her death and claims to his subordinates they must "honor" her death by fulfilling their mission. To the shock of everyone around him, Mace unleashes an OrbitalBombardment directly upon Japan, [[ThereIsNoKillLikeOverkill hoping to kill both Revi and Nechla]], who he knows is alive, single-handedly ruining any chances of diplomacy between Earth and spacefarers. Upon missing his intended target, Mace attempts to launch another bombardment, openly not caring if he kills everyone on Earth.
*** [[GreaterScopeVillain Satyajit Shyamalan]] is the [[CorruptCorporateExecutive CEO]] of Playmaker Industries, a corrupt neuroscience organization that weaponizes A.I. development to [[WarForFunAndProfit fuel regional conflicts across the globe]]. Murdering Sayaka Nakasugi's father to gain full control of the Nakasugi family research, Shyamalan tries to recruit Sayaka for her talents so he can achieve his goals of [[GodhoodSeeker becoming a god]] on Earth. In the AlternateUniverse where he succeeded, Shyamalan inadvertently wiped out all life in the universe in his avaricious desire to discover the multiverse and expand his power.
** ''Decode'' season 1: [[CorruptCorporateExecutive Satyajit Shyamalan]] has a [[SocialDarwinist philosophy]] of only the "Chosen" deserving life. Locating an alien weapon called the Ryunka, Shyamalan seeks to use it to "cleanse" the world. Murdering those in his way, Shyamalan later strangles the host of the Ryunka's grandfather to death and hooks the Ryunka up to a device of his own making to amplify its powers, killing many, many people with the intention of [[AGodAmI completely annihilating humanity save those he deems worthy of life]].
* CultClassic: The franchise as a whole isn't very well-known, but has its fair share of fans (including director Creator/ZackSnyder).
* DracoInLeatherPants: Averted for the most part with Shyamalan, who appears to be more hated than loved, likely because of his SmugSnake tendencies. Played somewhat straighter with [[spoiler: Nataru]]--yes he's deeply angry and upset about the treatment he received as [[spoiler: a "failed" Ixioran experiment]], and yes he sees the error in his ways, but that doesn't justify [[spoiler: brutally murdering the alien fugitives Birdy was told to bring into custody, even when they're not aggressive or begging for their lives.]]
* EnsembleDarkhorse: The two Yakuza guys from ''Decode''. They play no role in the plot whatsoever, being there only to set up the RunningGag about destroying yet another car of theirs.
* EvilIsCool: Notably averted in ''Decode'', where the evil deeds and philosophy of both Shyamalan and [[spoiler: Nataru]] are depicted very unglamorously and mostly just convey how ''screwed-up'' they are.
* HarsherInHindsight: [[spoiler: Shyamalan's treatment of Sayaka, with it [[DoesThisRemindYouOfAnything being played as if she were a rape victim]], became much more disturbing after Creator/ToddHaberkorn was accused of sexual assault.]]
* HilariousInHindsight:
** In the original manga, after getting caught by Gomez trashing some Arkazoids, with the help of Tsuotmu, Birdy rattles off a what could be seen as a precursor to the types of speeches given by Manga/SailorMoon (given the original manga predated ''Sailor Moon''). In the OVA, Birdy was voiced by [[Creator/KotonoMitsuishi Sailor Moon's seiyuu herself]].
** [[spoiler: Shyamalan's death at the hands of Sayaka after the Ryunka completely possesses her]] is a lot more unintentionally hilarious to watch when you remember that their seiyuu, Creator/KenichiSuzumura and Creator/MaayaSakamoto, are now married, which also augments the NoYay undertones between those two characters
** In the OVA series, Birdy is followed by someone who turns out to be a talent scout, thinking she could be a model. In ''Decode'', Birdy has a disguise as one.
** There's an episode in which a little girl who defends a boy from bullies at a refugee camp Tsutomu and his friends visit sparks a debate among the boys about whether it's humiliating to have to be saved by a girl. In ''Anime/HeatGuyJ,'' an earlier work by Kazuki Akane, two of the important men have the following exchange:
--->You have to be saved by a woman? That's so pathetic.
--->It's not every day you get saved by an angel.
** Yutaka Izubuchi served as the creature designer for the OVA adaptation. He would also serve as the creative producer for ''Decode''.
** One of the tracks for ''Decode'' is named "Franchise/WonderWoman". Not only did Creator/ZackSnyder admit that ''Decode'' was an influence for the Superman/Zod battle at the end of ''Film/ManOfSteel'', but in the Franchise/DCExtendedUniverse, Creator/YukoKaida (Moss) is the dub voice actress for Wonder Woman and Creator/KotonoMitsuishi (Birdy herself in the OVA series) narrated a trailer for ''Film/WonderWoman2017''.
* MoralEventHorizon: [[spoiler: Nataru]] crossed this after killing one of the escaped aliens after she decided to leave the rest of the survivors in protest over their actions. To be fair, she left less in protest and more out of fear that Nataru would find her if she stayed with the group, but ''still.''
%%* {{Narm}}: The OVA's English dub is notoriously bad.
%%* NoYay: Shyamalan/''Sayaka''
* RetroactiveRecognition: Birdy's voice actress in the English dub of the OVA is Alex [=McCord=]. Yes, the same Alex [=McCord=] who'd later become one of the original cast members of ''Series/TheRealHousewives of New York City''.
%%* SoBadItsGood: The English dub of the OVA adaptation.
* {{Squick}}
** Tsutomu's death. Especially in ''Decode'', where he gets blown in half. In the OVA, he's electrocuted.
*** He's also electrocuted in the original manga. In the remake, he gets a hole blown into his torso.
** Geega's transformation in the OVA.
** In both series, Bacillus. [[spoiler: He bonds himself to several dogs at once in the OVA. In ''Decode'', his hosts visibly fall apart while fighting Birdy. His death in both the OVA (getting set on fire) and ''Decode'' (getting blown up) could also count.]]
** In the OVA, the aforementioned mad scientist's experiments.
** [[spoiler: The escape of several aliens in the opening to the second season of ''Decode'' involves them killing the guards in goresome fashion. The subsequent deaths of several of said aliens in also horrific.]]
** [[spoiler: Violin's death in both series. While she suffered a severe head blow in the OVA, in ''Decode'', her head gets crushed in.]]
** Shyamalan's treatment of Sayaka, because of the NoYay.
* TooBleakStoppedCaring: Some fans found the second season of ''Decode'' a little too BloodierAndGorier and DarkerAndEdgier, especially with [[spoiler:the FantasticRacism suffered by the Altans, Nataru being a self-loathing serial killer, and the origins of Birdy as a genetically-engineered SuperSoldier designed to be a cop due to said racism.]]
%%* ToyShip: Marina and Takumi from ''Decode 02'' episode 3.
%%* TheWoobie:
%%** Birdy herself once we learn more about her past.
%%** In fact, most of the characters who haven't led a thoroughly normal life seem to have at least been this when young.
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