Atlantis (アトランティス) is an Akuma Chojin that fought and killed Robin Mask.
Atlantis was an Archerfish-like chojin who had mental control over liquid and became stronger when he fought underwater. He first fought Robin Mask and gained the upper hand, killing his opponent when he lured Robin underwater by throwing Meat's body part into the lake on which the ring floated. He did a number on Kinnikuman as well, but ultimately Kin defeated him. He was one of the chojin to escape from Hell and be retrieved by Omegaman Dexia.
Atlantis makes a return to fight one of the Perfect Large Numbers, Marlinman. Despite his struggle against the marlin Chojin, he had a boy cheer for him even though Atlantis is an Akuma Chojin. This gives him the resolve to fight back against Marlinman and end the match with one of Robin Mask's finishing techniques, the Tower Bridge. The match sadly ends with a draw as Atlantis had too many fatal wounds.
Atlantis first appears alongside Buffaloman and the other Devil Chojin after the 21st Chojin Olympics.  He was sealed away with six other chojin, due to their excessive level of violence and brutal fighting techniques, and was sealed away - by 100,000 chojin - into a space "roach motel", which acted as a prison. 
Kinnikuman - during a celebration of his victory in the Olympics - is thrown so high that he strikes a button on their makeshift prison, which releases them. They travel to Earth to disturb a Chojin Fan Appreciation Event, and steal parts of Meat Alexandria's body in order to force Kinnikuman into a competition against them. 
He announces that Kinnikuman is too injured to fight, so the remaining Devil Chojin should fight against the remaining Justice Chojin.  Robin chooses Atlantis for his opponent.  He fights Atlantis on a special ring on a lake in Ueno, where Atlantis surprises Robin in the ring before attacking from behind.  Robin starts strong, as he manages to counter Atlantis, but Atlantis ultimately dives into the waters. 
He follows with high speed into the lake, as he rapidly kicks at Atlantis' head, but he is eventually knocked away by a Magnum Canon. Atlantis tries to force Robin into the lake with his Magnum Canon, but the ropes stretch and Robin is able to use those to jump away. He proceeds to ride the Magnum Canon, until he lands a Drop Kick to the face. Atlantis then throws Meat's leg into the lake. This causes Robin to abandon his strategy, as he dives into the lake to save Meat's leg from harm. 
Atlantis follows him and proceeds to strangle him. 
Alisa arrives to support Robin, at which point he attempts a Pile Driver. This creates two whirlpools, as the power of Atlantis and Robin collide, and then - after several seconds of silence - Atlantis emerges from the lake with the mask of Robin Mask in his hands. It is revealed, after rescuing Meat's right leg, that he was trapped within an Atlantis Driver. Alisa clutches Robin's mask in grief, while Kinnikuman retrieves Meat's leg. 
Later Kinnikuman fights against Atlantis.  Atlantis begins with a Water Magnum, but Kinnikuman uses Salmon Swimming Stream to swim up the beam of water, and headbutts Atlantis in his face. Kinnikuman attempts a body-press, but the spirits of his deceased opponents hold him back: The Mountain, Stecasse King, Mr Khamen, and Black Hole. He thus can't move and lands on Atlantis knees. He tries to put Atlantis in a sleeping hold, but Black Hole cuts into his neck. Mongolman reveals that this is due to a Blood Bind, and he takes Terryman and Brocken Jr. into the spirit world to defeat the spirits. 
Kinnikuman is thrown into the lake by Atlantis.  Due to his friends defeating the spirits, Kinnikuman is able to swim upwards and jump back onto the ring.  Atlantis jumps into the water and covers the ring in a thick fog, which enables him to trick Kinnikuman into thinking the corner-post is him and striking his head against it in the confusion. Atlantis uses a water magnum, which destroys some of the ropes, and then hits him with a Water Ball. He follows this with a St Helen's Eruption. 
Kinnikuman uses his Fire of Inner Strength to escape the hold, and a Muscle Typhoon to get rid of the mist.  In order to avenge Robin Mask, Kinnikuman use a Tower Bridge attack on Atlantis, at which point Atlantis tosses Meat's right leg into the leg. Kinnikuman jumps in to save the leg, as Atlantis follows, but uses a U-Boat technique against him.  Buffaloman convince Kinnikuman to finish using his Kinniku Buster, which breaks Atlantis' back, neck, and hip-bones.  This defeats At;antis and allows Kinnikuman to retrieve the leg. 
(More to Come)
- Water Magnum (ウォーターマグナム)
- An Archerfish-like high-pressure water cannon from his mouth.
- Water Ball (ウォーターボール)
- Atlantis chucks a ball made out of water at his foe.
- Atlantis Driver (アトランティスドライバー)
- A Pile Driver that is performed underwater.
- Devil Necromancy Blood Bind (悪魔霊術血縛り Akuma Reijutsu Chi Shibari)
- The blood of the fallen Devil Chojin (Stereo Cassette King, Black Hole, The Mountain, and Mister Khamen) on Kinnikuman's body cause their spirits to revive and hold him in place while Atlantis attacks him.
- Mt. Saint Helens Eruption (水芸セントヘレンズ大噴火 Mizugei Sento Herenzu Dai Funka)
- Atlantis places the foe in a chokehold and squeezes hard until blood squirts out of their forehead, causing them to die from blood loss. It's changed to water in the anime, and their death is caused by dehydration instead.
- Atlantis Mist (アトランティスミスト)
- Atlantis spreads his arms and a mist covers the arena. Atlantis can use this to launch sneak attacks on the foe.
- Neck Cut Drop Kick (ネックカットドロップキック)
- Tower Bridge (タワーブリッジ)
- An imitation of Robin Mask's signature back-breaker technique done out of respect.
- One of the 7 Devil Chojins
- Win/Loss Record
|General Devil, Satan|
|Seven Devil Chojin|
|Buffaloman, Springman, Atlantis, The Mountain, Mister Khamen, Black Hole, Stereo-Cassette King|
|Six Devil Knight|
|Asuraman, Sunshine, The Ninja, Junkman, Planetman, Sneagator|
|Omega Centauri Six Spears|
|Omegaman Aristera, Hailman, Pirateman, Gear Master, Mariquitaman, Lunaight|