Doraemon: Nobita's Great Battle of the Mermaid King is a 2010 anime film and part of the long-running Doraemon franchise.
Nobita, after being envious of Suneo boasting of his snorkeling vacation in Palau, convinces Doraemon to bring him on a snorkelling adventure as well. Doraemon decides to use his Underwater Pump Simulator gadget, combined with his Underwater Experience Glasses, to bring Nobita on an impromptu virtual snorkeling experience by linking the waters of Palau into Tokyo.
All seems like fun, until the gadget accidentally summons a great white shark and a mermaid into Japan. Doraemon, in a desperate attempt to get rid of the shark, decide to reverse the simulator's effects and have all summoned marine life sent back to the oceans, but the mermaid, Princess Sophia of the Aquarians, gets stranded in Nobita's backyard. When Nobita and friends attempts to return Sophia to her world of Aquaria, becoming close friends to Sophia in the process, they discovering an evil Merman warlord - who destroyed Planet Aquaria of the Merpeople 5,000 years ago - is coming to seek a magical sword in Sophia's possession to take over the oceans.
A manga adaptation is released around the same time as the movie, published by Shogakukan. And despite coming out a month before the movie, the manga is based on the film due to the film's script coming into existence first.
Contains numerous parallels in themes and storyline as Doraemon: Nobita and the Castle of the Undersea Devil, an earlier underwater adventure in the franchise.
Doraemon: Nobita's Great Battle of the Mermaid King contain examples of:
- Adaptation Deviation:
- Sophia's identity as a mermaid is exposed when Shizuka tries taking her clothes to the dryer and accidentally activates the mermaid buckle, turning into a mermaid. In the manga it's Doraemon who accidentally activates it while searching for clues regarding Sophia's backstory (and was later scolded by Shizuka for "snooping through girl's clothing").
- The movie have Sophia's inheritance of the throne from Undine occuring before the battle against Bulkin. In the manga it occurs after the climax when all the action is over. She gets crowned either ways.
- Bulkin doesn't realize the Mermaid Sword is a fake until the gang is out of his sight; in the manga, a slip-up from Haribo alerts Bulkin that the sword is a counterfit.
- Adaptation Expansion:
- The first half of the story is based on "Underwater Pump Simulator", a short from the manga, where Doraemon uses the titular gadget to create a simulated underwater environment after Nobita wants to go on a snorkeling adventure, dragging in a bunch of marine life that Doraemon later ejects back into the ocean. But the film added a subplot about Sophia the mermaid getting summoned as well, kickstarting the adventure.
- There's also a minor sub-plot borrowed from "The Jaws in the Open Lot", a manga chapter where Doraemon's gadgets accidentally summoned a great white into Tokyo.
- Adaptational Jerkass:
- The manga does this to Shizuka, of all people. She insists on giving Sophia a scrubbing after finding out Sophia never heard of the concept of a "bath" while saying the people of Sophia's world needs to be "educated on cleanliness", never mind the fact that Sophia is obviously not of this world (given how she doesn't recognize an airplane when she sees one) and later on nags on Doraemon for snooping around Sophia's clothes.
- Dorami gets a somewhat similar treatment in the manga, demanding that her brother gives her twenty Melon Buns in exchange for her service. Later on she interrupts the gang's adventure in Aquaria, telling them she have important information - but Doraemon needs to give her five more buns in exchange. In the anime film she voluntary helps her brother and the gang.
- Almost Out of Oxygen: Shizuka nearly suffers this fate when she's abducted by Tragis and used as leverage to exchange for the Mermaid Sword. Early on as the gang are on their way to make the swap, Nobita comments that he's suddenly feeling ill. Gian and Suneo had the same reaction, at which point Doraemon remembers the Adaptation Light's effects he applied a day earlier, which lasts only for 24 hours, is almost out, and while he re-applies the light on Nobita and the others (and himself), they realize the same fate will happen to Shizuka within a handful of minutes. Luckily, Nobita made it on time and re-applied the Light on Shizuka with 0.93 seconds to spare.
- Animal Mecha: Bulkin's army has giant ships built based on fishes. Entire fleets of them.
- Big Bad: Bulkin is a merman warlord who have intentions of conquering the underwater world by retrieving the all-powerful, sacred Mermaid Sword, which gives him control of the seas and abilities to create tidal waves with every swing.
- Bookends: And a fun Brick Joke over the Doraemon / Dorami siblings' Iconic Trademark Favourite Food(s). Near the start, Doraemon is sent on a shopping errand by Tamako because Nobita isn't around. Half-complaining over his chores, Doraemon suddenly realize the shopping list contains "Dorayaki for Doraemon", which makes him exclaim "Thanks mom, I love you!"... at the end of the film, Nobita and Doraemon are both not around, so Tamako sends Dorami on another shopping errand, only for Dorami to realize the shopping list include "Melon buns for Dorami", making her exclaim "Thanks mom, I love you!"
- Chekhov's Gun:
- Nobita's toy inflatable sword that he intends to throw away in anger, only to change his mind in the last second and shove it into his pockets. When the gang needs to create a fake sword with the Instant Pearl Machine in exchange for Shizuka's life, Nobita remembered he still have his toy. What's even better is that the toy is later inflated again by Gian, the same person who deflated it in the first place!
- The Tsunami Button on the Underwater Pump Simulator, which Nobita accidentally triggers in a What Does This Button Do? moment, turns out to be useful in the final battle against Bulkin in order to take him down for good.
- Clothes Make the Superman: Sophia and her fellow Aquarians can turn into mermaids thanks to their transformation uniforms, via a knob on the belt that can be activated with a single touch. It applies on humans as well, like when Shizuka tries taking Sohpia's clothes to the washer while Sophia is bathing... only to accidentally move the knob and turn herself into a mermaid.
- Continuity Cavalcade: For the manga only, during a flashback the gang's adventures from Doraemon: Nobita's Dinosaur, Doraemon: The Record of Nobita : Spaceblazer, Doraemon: Nobita and the Green Giant Legend and Doraemon: Nobita's Great Adventure into the Underworld could be seen in one single panel. This however causes a minor Continuity Snarl - the events of Underworld shouldn't be included as it's from an alternate universe where only Doraemon, Nobita and Dorami could've remembered the events.
- Cool Sword: The Mermaid's Sword, a claymore with a jewel in it's hilt and emits a powerful golden aura when being used. It can also create tsunamis and tidal waves with each swing, which Bulkin covets in his quest to dominate the seas.
- Face Fault: When Bulkin starts his rampage sending tidal waves across the ocean, the gang asks Doraemon what gadgets they can use to reach and counter the villain. Doraemon pulls out a bunch of surfboards from his Fourth Dimensional Pocket, which Nobita exclaims it must be some "cool futuristic surfboard gadget"... nope, they're ordinary surfboards. Everyone present quickly did a fault.
- Fantastic Racism: Most of the Aquarians really doesn't trust the surface people, but even moreso for Sophia's lieutenant, Haribo, who immediately accuses the gang for "kidnapping the princess" and sentence them to be fed to a Megalodon!
- Flanderization: The manga tie-in based on the anime (not within the film itself, thankfully) somehow blows Shizuka's obsession with baths to ridiculous proportions. In the original stories Shizuka is a Bathing Beauty who likes washing herself more than the other characters, but the tie-in manga has Shizuka actually forcing Sophia into a bubble bath and scrubbing her while lecturing Sophia about the "importance of baths", and that she thinks the entire population of Aqua needs to be educated over the necessity of bathing (after Sophia accidentally reveals baths doesn't exist on her home planet, never mind Aqua is a Single-Biome Planet covered in water and her populations are merfolks). On the first night the gang and Sophia spends together in Doraemon's Underwater Tents, Shizuka somehow feels the need to let out a stern reminder at Sophia, "And don't forget to bathe!"
- The Great Flood: Invoked, when Doraemon's Underwater Pump Simulator gadget unleashes an unstoppable deluge that floods Tokyo with "simulated" water. These can only be seen by wearers of the Underwater Experience Glasses, ordiniary people wouldn't feel a thing, but from the perspective of Nobita and Doraemon atop a skyscraper's roof (wearing those glasses) they saw the entirety of the city covered with water. What's even better is that it's impossible to drown in these waters.
- I Have Your Wife: When Tragis abducted Shizuka while mistaking her to be Princess Sophia, he instead decide to use Shizuka as leverage in exchange for the Mermaid Sword, demanding the gang to either surrender the weapon, or he'll eledctrocute Shizuka.
- Home Field Advantage: The Mermaid Sword, while unstoppable underwater, have a Weaksauce Weakness where it's useless on land. For the movie's final confrontation, the gang uses the Underwater Pump Simulator to trick Bulkin - then armed with the unstoppable sword - on a beach, where he's bewildered by his weapon being suddenly useless before the gang unleashes a tsunami on him.
- Mistaken Identity: Bulkin's dragon, Tragis, unintentionally abducts Shizuka after mistaking her to be Princess Sophia, because she happens to be wearing the princess' tiara, one that Sophia good-naturedly lent her because Shizuka "always wanted to feel how it's like to be a princess". Naturally Sophia's My God, What Have I Done? reaction is quite apparent.
- No More for Me: Early in the film, a drunk Nobisuke, staggering his way home, saw a school of fishes summoned by the Underwater Pump Simulator swim past. While he's on foot. Cue Nobisuke shaking his head and believing he's seeing things from drinking.
- Non-Fatal Explosions: During the defense of Aquaria, both Doraemon and Dorami attempts to fend off Bulkin's forces with their gadgets, only to be overwhelmed and hit by a dozen stray energy bolts which explodes right in front of them (while underwater!), but doesn't seem to leave any lasting damage, besides both robot cats having an Ash Face that goes away in the following scene. Maybe because they're robot cats and far more durable than humans?
- Our Mermaids Are Different: Sophia and her kin are former humans who became adapt to living underwater, with their mermaid transformation being facilitated by turning a button on their clothes. They can survive on dry land for quite a while, but the moment they start drying up they'll need to submerge themselves in water, notably in Sophia's first meeting with the gang - she passes out after flying for several minutes on the Takecopter, but luckily the tub at Shizuka's house is always full of water.
- Running Gag: Doraemon getting mistaken for a pufferfish by other characters, causing him to angrily retort he's an "underwater robot cat".
- Single-Biome Planet: Downplayed with Sophie's home planet, Aqua, which is almost 90% covered in water. But there are small islets and pockets of land around, with Bulkin's defeat taking place on a beach.
- Slippery as an Eel: In Aquaria, the gang gets attacked by a behemoth-sized rampaging eel, which nearly devours them if not for Gian finding a Convenient Cranny for everyone to hide in. Said eel monster was actually a harmless, normal-sized moray eel, who grows giant-sized and unstoppably violent after Tragis attached a genetic-manipulating gadget on it.
- Threatening Shark: The royal merpeople keep a living megalodon which they feed criminals to.
- Under the Sea: Thanks to Doraemon using his Duplication Mirror on Sophia's outfit so everyone can be mer-folks, most of the adventure takes place underwater as the gang explores Sophia's Underwater City hometown of Aquaria.
- Underwater Ruins: Most of the movie takes place in the ruins outside the underwater city of Aquaria, including a battle between the Aquarian (backed up by Doraemon's gadgets) and Bulkin's army.
- What Does This Button Do?: When Doraemon displays the ability of his Underwater Pump Simulator, Nobita sees a glowing button on it's tip and asks what it does while touching it, before Doraemon can stop him. Turns out said button can create indoor tsunamis. It's one of the Chekhov's Gun moments the film employs later on.