''Blood Seal ~Eternal Mermaid~'' is the twenty-third MadeForTVMovie in the ''Anime/LupinIII'' anime franchise. It debuted on December 2, 2011 to a modest viewing audience.

Made to celebrate the 40th Anniversary of the ''Lupin III'' franchise on television, the special brought a number of changes to ''Lupin''. The first notable one is the major art style changes to the ''Lupin'' characters; past specials for the last decade had relied on designs largely derived from ''Shin Lupin III'', the second TV series. TMSEntertainment (originally Studio Telecom), who was involved with the early days of ''Lupin'', was brought back to do the animation for ''Blood Seal'', and accordingly the designs were redone to evoke the early years of the first "green jacket" ''Lupin'' series and the proto-StudioGhibli designs used in ''Anime/TheCastleOfCagliostro''.[[note]]TMS has always controlled the ''Lupin'' franchise (at least on the anime side). However, over the years they simply outsourced production to other studios rather than handling any animation in-house.[[/note]]

The second change was the first major shakeup of the ''Lupin'' cast since Kan'ichi Kurita took over the role of Lupin in ''Anime/FarewellToNostradamus'', following the death of original seiyuu Creator/YasuoYamada. It was announced with this special that the long-time voice actors for Zenigata (Creator/GoroNaya), Fujiko (Creator/EikoMasuyama), and Goemon (Creator/MakioInoue) had retired; they were replaced with Creator/KoichiYamadera, Creator/MiyukiSawashiro, and Creator/DaisukeNamikawa, respectively. With this cast change, Creator/KiyoshiKobayashi, who plays Jigen, is the only original ''Lupin'' voice actor remaining.

The movie opens with Lupin being ordered at gunpoint by crime boss Toudou to steal a precious gem, the Mermaid's Scale, at an upcoming black market auction. Although he succeeds, things go badly wrong when a bomb goes off shortly after he departs. In addition, a perky and persistent 14 year-old popcorn vendor and would-be thief, Maki, begs Lupin to make her his apprentice in crime. Combined with another gem, the Dragon Scale, owned by the sinister head of a medtech company, a mysterious waif of a girl who seems to defy death, and a treasure that Lupin's own grandfather seemingly failed to steal, the gang becomes tangled in a dark and mysterious plot for the treasure of mythological figure Yao Bikuni... and possibly the secret of immortality itself.

'''Complete spoilers below''' -- don't read further if you don't want to know how this caper turns out!
!!This TV movie features examples of:
* AbsurdlySharpBlade: Goemon goes about cutting impossible things into tiny pieces with his usual aplomb.
* AlcoholicParent: How Maki ends up in a children's home.
* ArmsDealer: Himura, who plans to use the secret of Bikuni's descendants to make immortal soldiers.
* BigBad: Toudou is ordering Lupin around as the introduction of the movie. She is quickly killed off, though, and the real big bad is shown to be Himuro.
* BikerBabe: Fujiko spends the last half of the film on her motorcycle.
* BloodlessCarnage: Averted, rather unusually. This is easily the bloodiest entry in the ''Lupin'' franchise.
* BloodMagic: It's there in the title.
* ChronicBackstabbingDisorder: Fujiko switches sides at least four different times.
* {{Determinator}}: Lupin. Even after he is hurt, he persists in going after Misa and hunting for clues of Lupin I's theft attempt.
* DualWielding: Kageura.
* FamousAncestor: Lupin I plays a role in the overall plot. In addition, both Misa and Himuro are descended from Yao Bikuni, a famous character in Japanese mythology.
* FairWeatherMentor: Lupin to Mika. It's on purpose, though; he doesn't want Mika to turn to a life of crime like him.
* FemmeFatale: Fujiko, as usual.
* GenkiGirl: Mika.
* HealingFactor: Misa, inherited from her ancestor Bikuni. She loses it at the end of the special when Bikuni finally moves on. Himuro also temporarily gains it after injecting Bikuni's blood into him.
* HumanShield: Toudou uses Misa as one against Kageura. He simply runs them ''both'' through.
* IHaveBoobsYouMustObey: Fujiko pulls this on Lupin often. Lupin later reveals he was pretending so he could trick her instead.
* IOweYouMyLife: Jigen to Misa after she takes a deflected dagger that would have killed him.
* ImmortalitySeeker: Himuro. To the point he is willing to violate his bloodline's role as a guardian.
* IWillWaitForYou: Yao Bikuni for Lupin I (as represented by his grandson).
* MedicalHorror: Performed by Himuro on Misa and innocent human guinea pigs.
* MineralMacGuffin: The Mermaid's Scale and the Dragon Scale gems.
* NoGoodDeedGoesUnpunished: Misa offering to work off the children's home debt for Toudou brings her into contact with the even nastier Himuro.
* OneeSama: Misa for Mika.
* PsychoSerum: What Bikuni's blood does to Himuro.
* RemovingTheHeadOrDestroyingTheBrain: How Goemon and Jigen manage to finish the immortal Himuro off.
* ShoutOut: Misa's outfit is conspicuously close to Clarisse's casual garb from ''Anime/TheCastleOfCagliostro''.
* SpyCatsuit: Fujiko spends most of the film in one.
* StolenMacGuffinReveal: The gems Fujiko steals from Lupin are quickly found out to be fakes.
* SuperSerum: Himuro is trying to develop one. He later finds it in the blood of his ancestor Bikuni.
* SympatheticInspectorAntagonist: Zenigata never stops going after Lupin in this special, but he's also highly suspicious of Himuro and is bound to catch him in the wrong. He later (reluctantly) helps Lupin's gang after Himuro goes crazy.
* UnderestimatingBadassery: Himuro does this to Zenigata at first; Zenigata promptly throws the hulked-out Himuro over his shoulder. Himuro does not make that mistake again.
* WhoWantsToLiveForever: The view of Yao Bikuni, her lonely spirit trapped in a cave for centuries.
* YouMonster: Himuro. He experiments on and kills innocent men in attempting to gain the secret of Misa's superactive cells, has no issues with sending {{Mook}}s to their death, uses a fourteen year-old girl as a shield, and wants to profit on bringing immortal soldiers into the world.