It is 1949 in an Alternate History Japan and the mysterious thief, K-20 searches for a device based on technology created by Nikola Tesla that can transmit electricity anywhere in the world.
Our hero is Heikichi Endo (Takeshi Kaneshiro), a poor circus performer who is framed and arrested for K-20's crimes. Heikichi is broken out of custody by Genji and Kikuko, two ex-criminals who worked with him at the circus. They eventually convince Heikichi to train how to be a thief so he can fight K-20 and stop his plans. In his first direct confrontation with K-20, he stops him interrogating Duchess Yoko Hashiba, heir to the oil magnate who built the Tesla device and she joins their group. Unfortunately, Yoko is engaged to Baron Kogoro Akechi, the famous detective and far as the police are concerned she was kidnapped by Heikichi.
Tropes include:
- Alternate History: The film is set in a timeline where Japan never entered World War II and never abolished the Meiji era class divide. Most of the population live in poverty, barred from higher-ranking jobs because of which class they were born into.
- Antagonist Title: K-20 is definitely the villain of the movie. At least until Heikichi takes over the persona.
- Aristocrats Are Evil: The noble class abuse their privileged status over the underclass. There is even a shanty town of children orphaned by nobles who did not face any punishment for killing their parents. Yoko averts this and is shocked to see how the poor lives.
- Armies Are Evil: When the heroes need to use a special camera that is in possession of the military to locate the Tesla device, they decide to break in rather more straight forward methods for fear of military finding out about the Tesla device and turning it into a weapon.
- Arrow Catch: Part of Heikichi's circus act is dodging arrows, finishing with him catching one and pretending to be hit, only for a "miraculous recovery". These skills save Genji's life when he catches a blade shot from a booby-trapped safe.
- Bath of Poverty: When Yoko is bathing in Genji and Kikuko's home, she keeps asking if they have a shower and shampoo, the sort of thing that the poor circus performers are not able to afford. They don't even know what shampoo is.
- Beat Them at Their Own Game: In order to beat K-20, Heikichi trains in the skills of a thief. The books he learned the skills from may even be the ones that K-20 may himself used to train.
- Contrived Clumsiness: At one point, Yoko tries to delay Akechi by pretending to trip and spill a plate of food on to him. Akechi offhandedly catches the plate and the food on it without looking.
- Creator Cameo: Sō Kitamura makes a cameo when K-20 steals a smaller version of Tesla device.
- Criminal Mind Games: K-20 is cocky enough to send messages of what he is going to steal and challenges Akechi to catch him. Subverted when it is revealed that Akechi is K-20 and he sent the messages. He does this so his Akechi persona would be brought into protect against the crime and he would be at the center of any security around his targets.
- Doesn't Like Guns: Despite being the villain, K-20 says he detests using guns. He makes an exception to shoot Heikichi in the final fight. This backfires since he uses the gun Genji gave Heikichi which was a trick circus gun that only shot fake-blood paintballs.
- Faceless Mooks: The soldiers guarding the camera wear face-concealing balaclavas for no discernible reason. As one reviewer
said, it made them look like COBRA mooks. - Faking the Dead: Akechi fakes his own death using squibs to make it look like K-20 shot him.
- Frame-Up: Heikichi starts off as a poor circus performer and jumps at the opportunity when a man offers him a high paying Paparazzi job, so he can pay for the ringmaster’s medical bills. All he has to do is use his circus skills to get some photos of the wedding between Akechi and Yoko. Unfortunately, the man was really K-20 and he had planted explosives that are triggered by the camera he gave Heikichi. On top of that K-20 plants diamonds that he stole in Heikichi's sleeping quarters. This quickly leads to Heikichi getting arrested for being K-20.
- Gadgeteer Genius: Genji was a prop maker at the circus and is able to use his mechanical skills to equip Heikichi with various homemade gadgets. Also, he is able to rewire the Tesla device to target itself while K-20 and Heikichi are fighting.
- Grappling Gun: Genji builds a wrist-mounted grappling gun for Heikichi after he sees the injuries from his failure to jump a gap during his training.
- I Want My Beloved to Be Happy: Yoko offers to stay with Heikichi even though he would have to stay on the run. Heikichi turns her down rather than take her from her life.
- Just Like Robin Hood: Heikichi initially dislikes the idea to training to become a thief to combat K-20. It is not until he sees the poor shanty town that Shinsuke and his fellow orphans live in that he decides to train to be a thief so he can support them as well.
- Latex Perfection: The title K-20 or the longer version, Kaijin Nijū Mensō Den (roughly translated to The Fiend with Twenty Faces) comes from the thief's use of masks that perfectly disguise himself as other people. The police do not even known what K-20 truly looks like. He is caught out when Yoko recognizes his uncovered hands. Heikichi picks up some similar disguise skills during his own training.
- Legacy Character: An unwanted version. Heikichi is forced to take the identity of K-20 in the end as the police believe he is K-20 and the only man who could exonerate him, Akechi is dead.
- The Legend of X
- Le Parkour: Most of Heikichi's training consists of doing parkour run over the city. Mastering this somehow translates into learning Wire Fu.
- Malevolent Masked Man: When K-20 is not wearing one of his disguises, he wears a stern-looking black and silver mask.
- Nose Bleed: Heikichi and Genji walk in on Yoko while she is bathing and naturally she decides to stand up to scold them while stark naked. Kikuko chastises them both for getting nose bleeds at their age.
- Phantom Thief: K-20, even announcing his crimes ahead of time does not slow him down.
- Red Herring
- The creepy guy following Akechi around turns out not be K-20 but an agent of the government that is investigate whether Akechi is really part of nobility.
- Yoshio Kobayashi, assistant to Akechi gets many moments when it is hinted that he is K-20. He seems angry when Genji says Heikichi may surpassed K-20 in skill, he has an almost manic glee at the idea of K-20 using the Tesla device and happens to out of the room when Akechi is "shot". In the end it is all just a coincidence.
- Rescue Romance: Yoko starts to fall for Heikichi after he rescues her from K-20, unfortunately she is engaged to Akechi. Then Akechi turns out to be K-20 and is killed trying to activate the Tesla device.
- Sexy Surfacing Shot: Heikichi and Genji accidentally walk into Yoko during her Bathtub Scene, she ends up leaping out of the water to scold them while naked. The audience only sees her Shoulders-Up Nudity and Toplessness from the Back while they get the full frontal.
- Sheltered Aristocrat: Yoko does not seem understand that people would live in a small house because that is all that can afford and is shocked that there are orphans living on the street and the government is not doing much to help them.
- Staged Shooting: Akechi uses squibs to make it look like K-20 shot him so that they wouldn't suspect that K-20 was actually him.
- Tokyo Tower: Despite being set in 1949, the shots of the Japanese capital city of Teito include a rusting Tokyo Tower. Presumably the Tower was built earlier since Japan never participated in World War II.
- The Tunguska Event: The film follows on from the idea that Nikola Tesla caused the event during his experiments to broadcast electricity. Yoko's father, a Japanese oil magnate, was one of the surveyors of the Tunguska site in the Alternate History and he invested in Tesla's project. By the start of the movie there are devices resembling the Wardenclyffe Tower that can accurately transmit electricity to power devices or send lighting-like blasts.
- We Can Rule Together: In the final confrontation, K-20 asks Heikichi to join him in his plan, Heikichi calls him out on being no different to the people who control the world and turns him down.
- Well-Intentioned Extremist: K-20 was born to the lower classes and faked the records necessary to pretend to be a Baron using the proceeds of his crimes. His resentment of the society that forced him to do this subterfuge to join the higher ranks led him to the plan of using the Tesla device to destroy important places across the world and use his control of the power from the Tesla device to control what was left. He would then rebuild civilization without the social gap. His plans may have changed society for the better but would have killed countless people in the process and would have set himself up as dictator.
- Zeppelins from Another World: The opening shot is a few autogyros launching from a zeppelin over Teito.
