Characters from Doraemon: Nobita and the Castle of the Undersea Devil.
Buggy
A sentient racecar capable of traveling underwater created by Doraemon specifically for helping the gang tour the bottom of the oceans.
- Big Damn Heroes: Showing up in the climax to save Shizuka from execution is one thing, but defeating Poseidon and ending the decades-old threat that is the Bermuda Triangle? Awesome.
- Eat Me: How he managed to defeat Poseidon in the climax, by forcing his way into Poseidon's mouth as he's about to explode.
- Flipping Helpless: Buggy is completely helpless once he's flipped around on his back, which is how Doraemon and Nobita restrains him when he start misbehaving.
- Morality Pet: The only member of the main cast Buggy isn't a dick towards is Shizuka, because she is the one person in the gang who's nice to him.
- Sentient Vehicle: A sentient racecar.
- Taking You with Me: Part of his Heroic Sacrifice; as Buggy barged out of Doraemon's Fourth Dimensional Pocket, one of Poseidon's nearby robots fires on it, hitting Buggy's back. Before Buggy explodes, he shoves himself into Poseidon so the mad AI - and the rest of the hostile robot army - goes down with him.
Kingdom of Mu
A benevolent kingdom of underwater folks who bears some Fantastic Racism towards the surface people. After they rescued Doraemon and gang from a giant squid attack, the gang find themselves in Mu, tended by a young Mu knight named Eru, just as the Mu council is debating whether they should allow the gang to return to the surface or stay forever in Mu.Eru
"Good morning, I see you have woken up."
A young Mu knight who saves Doraemon and gang from a giant squid. Later serves as the heroes' main companion for the adventure.- Adaptation Dye-Job: He's blonde in the anime version, despite having dark hair in the manga.
- Child Soldiers: He's a couple years older than Nobita and gang, but he's already serving the Mu military as a knight and warrior.
- Hair of Gold, Heart of Gold: In the anime only, but he is one of the only Mu resident who isn't outwardly hostile or suspicious towards Nobita and the surface folk.
- Heroes Prefer Swords: And how - the final raid have Doraemon and the boys using Doraemon's assorted collection of gaggets, but Eru does fine wielding his trusty sword.
- Nice Guy: He's actually the only Mu resident who isn't outwardly hostile towards Doraemon and the other surface people, and in fact asks for Doraemon, Nobita and Shizuka to treat his home like it's theirs. Too bad the Mu government have no intentions of letting the surface folk leave.
- Reused Character Design: His manga incarnation is just Dekisugi with longer hair and in knight armour. Looking at panels out of context it looks like Dekisugi is finally a member of the Long Tales series.
Atlantis
An ancient, underwater kingdom and an enemy of Mu, whose robotic forces threatens the safety of both the underwater world and surface.Kochi / Poseidon
"No one shall survive my wrath!"
- A.I. Is a Crapshoot: Kochi, having abandoned the Mu civilization and stole their technology to establish his own robot kingdom, decides to transfer his conscience into a machine called Poseidon capable of controlling his army, programming it to conquer and annhilate. Even after Kochi's death, Poseidon still continues to exist as a threat, waging war on Mu, killing plenty of Mu warriors and destroying ships and planes crossing the Bermuda Triangle.
- Been There, Shaped History: Kochi's escape from Mu and establishing his facility to dominate the world, as well as transferring his conscience into a robotic body called Poseidon, spawned the myth of Atlantis and the Bermuda Triangle legend, where his war machines are responsible for the disappearance and destruction of various ships in the legends.
- The Bermuda Triangle: Where Kochi fled after abandoning Mu, and establishes his own kingdom of machines while ruling as Poseidon.
- Derelict Graveyard: Atlantis is located right smack in the middle of one of these, belonging to planes, ships and other vehicles sunk by Kochi's / Poseidon's army of machines, of both human and Mu origin. Doraemon and gang have to cross these and it doesn't look pretty at all.
- Big Bad: Kochi (and later in his Poseidon incarnation) is the main villain of this adventure.
- Evil Genius: As Kochi, a ruthless, sinister Mu scientist who stole technology from his homeland and started all the mess.
- Flying Face: Poseidon appears as a single, hovering head of a sea-god in a throne room.
- Keystone Army: After Buggy pulls an Eat Me and took down Poseidon, his legion of machines and robots immediately comes to a standstill.
- Load-Bearing Boss: The death of Poseidon causes Atlantis to slowly and gradually collapse. Doraemon and Shizuka, escaping the throne room after Buggy's Heroic Sacrifice, quickly finds Nobita, Suneo, Gian and Eru in the dungeons and bails as the place goes down around them.
- Mecha-Mooks: Poseidon's army consists entirely of mechanical Fish People.
- Not So Stoic: Poseidon, despite his power, visibly panics when Buggy makes a beeline at him.
- Orcus on His Throne: Due to the real Kochi being dead and transferring his will into a floating robot head, Poseidon, for the entirety of his screentime Poseidon is just this floating mechanical head in his throne room, surrounded by his mooks.
- Posthumous Character: Kochi died several decades before the story even begins, but his creations, under his programming, continues to exist and complete his unfinished goals in dominating the seas.
- Robot Master: Kochi creates the robot army with stolen Mu tech, transfers his consciousness in a machine called Poseidon and controls his robots and machines in dominating the underwater world.
- Throat Light: In the anime, Kochi-as-Poseidon visibly emits a shining glow when he talks.
