Mysterious Beings/Monster Association

The Monster Association (怪人協会, Kaijin Kyōkai) is a group of Mysterious Beings led by Gyoro Gyoro and Monster King Orochi. Their base is located beneath Z-City. '''The following section contains Webcomic spoilers. You have been warned manga-only readers.'''  After its base is raided by the Hero Association, the Monster Association collapses.

Overview
The Monster Association consists of around 500 monsters, about 30 of which are disaster level Demon or higher. The boss (ボス, Bosu) is the Monster King, Orochi, although the organization is actually overseen by the military advisor (参謀, Sanbō), Gyoro Gyoro. Below them in ranks are the executives (幹部, Kanbu) who are specially promoted by Gyoro Gyoro.

The Monster Association is founded on the belief that one monster alone will eventually fall, but all of them together can defeat the heroes. Many monsters believe that they are stronger than the heroes; Gyoro Gyoro has to remind them that this will be their downfall, though sometimes she uses this to her advantage.

The goal of the Monster Association is to end the Hero Association and create a world of monsters ruled by Monster King Orochi. However, most members only joined forces for the former and do not view Orochi as their king, but they do acknowledge his great power. The plan is to lure the Hero Association into a decisive showdown. There are three primary objectives that are required to make this plan feasible:
 * 1) Strike fear to the human population through monster rampage.
 * 2) Kidnapping important hostages that are vital to the operation of the Hero Association.
 * 3) Transform powerful humans into monsters to boost military strength of the organization.

New monsters are recruited by offering Monster Cells to strong humans, such as the martial artists of Super Fight. Whoever eats the cells transform into a monster, but it has to be eaten raw. Typically they are eaten one per person, as eating more can result in failure and death. A Dragon-level monster born from the Monster Cells is considered a "huge success." Other monsters can join the Monster Association by going to the base beneath Z-City and meet with Gyoro Gyoro.

Disaster level is everything to the Monster Association. Gyoro Gyoro assesses each member and assigns them a level. The executives are monsters that earned the level of Dragon. Lesser monsters have the utmost respect for the executives and fear provoking them.

Outside of the executives, there are at least three other monsters that have reached the level of Dragon: Gale Wind and Hellfire Flame are Demon-level in their human forms, and Dragon-level in their monster forms; they are executive candidates but claim to not care for their ranks. The monster acting as middle management, Phoenix Man, was originally Demon-level, but became Dragon-level upon resurrecting.

Members are not permitted to kill each other as it will weaken the organization, although Gyoro Gyoro admits that this is difficult to enforce. Many of the monsters are hostile to each other. Presumably, this only applies to strong monsters since Gyoro Gyoro herself treats weak monsters as expendables and sometimes feeds them to Orochi. Even Demon-level monsters are not safe: Orochi ate Awakened Cockroach for losing, and Gyoro Gyoro used Rhino Wrestler as bait. Monsters with useful abilities, such as Do-S, are somewhat protected.

Vampire (Pureblood) claims to be the only Natural Type monster in the association.

History
The Monster Association is an unknown group founded by Gyoro Gyoro and Orochi. The headquarters of the Monster Association was previously the home of the Subterranean People who were all slaughtered.

Its leader, Orochi, defeated the martial artist Gouketsu and recruited him as a member.

The ninjas, Gale Wind and Hellfire Flame, joined to kill the hero Flashy Flash.

2 years ago, Elder Centipede joined to avenge his defeat against Blast.

Rumored Monster Arc
Rumors spread that strong monsters have been meeting up in Z-City's ghost town and that Humans and even some Mysterious Beings were avoiding the location.

Monster Raid Arc
In S-City, Venus Mantrap and Junior Centipede attack a sushi restaurant where the Hero Association benefactor Narinki and his son Waganma are dining. Metal Bat, who is guarding them, easily defeats both monsters.​​​​ Rafflesidon and Senior Centipede then emerge from the ground. Narinki and Waganma are knocked out by Rafflesidon's gas. Metal Bat fights the monsters, but is slightly sedated by the gases the monster released. He manages to break out of its control by smashing his head, arousing his fighting spirit, and kills both monsters with one strike each.

Moments later, Elder Centipede, a monster with threat level Dragon, emerges through the ground. Elder Centipede ignores Metal Bat's attacks and goes for Narinki. As Elder Centipede is about to catch the sponsor, he is struck by Metal Bat, and tries to shake Metal Bat off by maneuvering around the city. Elder Centipede manages to launch Metal Bat away and continues to rampage through the city. Just as Elder Centipede corners the heroes Pineapple and Mohican, who are carrying Narinki and Waganma, it is attacked by Metal Knight's missiles. Phoenix Man, Sludge Jellyfish and Rhino Wrestler then corner the heroes and demand the sponsor. After Garou finishes his fight with Metal Bat, Phoenix Man and Sludge Jellyfish discuss how they could use him to their advantage. After Metal Bat was knocked out by Zenko, Sludge Jellyfish tries to take her as hostage, but was struck by Garou. The monster was able to regenerate itself and Phoenix Man attempts to invite Garou into the Monster Association. Garou rudely declines by ripping up the invitation card. The monsters say they'll overlook Garou's rude behavior this time and promise that they will meet again if Garou continues to hero hunt. Meanwhile, Rhino Wrestler fights and defeats Pineapple and Mohican, and takes Waganma hostage. The monsters then retreat after explaining how fighting Metal Knight would only be in vain for them. The monsters retreat, but Metal Knight manages to stick to Elder Centipede and follow them to their base.

The Monster Association orchestrates simultaneous attacks many cities:
 * W-City: Heavy Kong fights against Marshall Gorilla.
 * D-City: Lightning Genji fights Maiko Plasma and Electric Catfish Man.
 * I-City: Hundred-Eyes Octopus wreaks havoc on the city
 * Y-City: Eyesight wreaks havoc on the city.
 * V-City: Pureblood wreaks havoc on the city.
 * Unknown city: Do-S and Free Hugger wreak havoc on the city.

Fist Fight Djinn was fighting the A-Class hero Smile Man, when Bang arrived at the scene. Fist Fight Djinn attempted to attack Bang, but was mercilessly killed by the S-Class hero. Meanwhile, Do-S managed to defeat many heroes and was then confronted by Fubuki and her Blizzard Group. Marshal Gorilla managed to defeat Heavy Kong and tells the civilians to spread the word about him. Maiko Plasma and Electric Catfish Man fought Lightning Genji and managed to hospitalize him. Hundred-Eyes Octopus kept devouring buildings and easily managed to defeat Death Gatling, Butterfly DX and Bone. Eyesight managed to poison Ecolo G and other heroes and fought Studless. Pureblood managed to kill many civilians.

Many monsters that appeared in C-City were defeated by Genos and Face Ripper later encountered the hero. Face Ripper managed to damage Genos, but was caught off guard and killed. In the same city, Awakened Cockroach defeated many heroes and meets Genos in an alley. On the TV, it was reported that Lightning Genji was defeated by the monsters, while Awakened Cockroach managed to have the upper-hand in the fight against Genos, but was caught in an adhesive trap, though he managed to escape before being struck by Genos' blast.

Do-S managed to transform all of the Blizzard Group members into her love slaves. While Fubuki was preoccupied by the love slaves, Do-S managed to pierce through her telekinesis and whip Fubuki. Do-S managed to hit Fubuki multiple times and believing that she had Fubuki's mind under her control, she revealed her plan of using Fubuki to lure Tatsumaki out. However, Do-S was sent flying and attacked by Fubuki. Angered she decided to kill Fubuki. When the area began to rumble, a monster falls in front of Do-S ans warns her about Tatsumaki. Frightened, Do-S orders her love slaves to distract Tatsumaki, while she escapes.

Super Fight Arc
The Monster Association continued their attack. Sweet Mask's concert was interrupted, the hospital where Mumen Rider, Tanktop Master and the Tank Topper Army were staying was attacked and Nyan broke into Smelly Lid Prison in search of Puri-Puri Prisoner. At their hideout Gyoro Gyoro and Monster King Orochi were discussing their invasion and Gouketsu's whereabouts. They managed to defeat S-Class heroes like Genos and Metal Knight, whose robot was hanging in chains severely damaged and captured at Monster Association's Headquarters.

Despite their success, many monsters were killed by S-Class heroes. Drive Knight easily killed some members and interrogated the last living one about the invasion. Child Emperor used Underdog Man No. 22 to fight Eyesight, but the monster was later eaten by Pig God. Hundred-Eyes Octopus's destruction forced to assemble an A-Class heroes team, but was later blinded by Flashy Flash and crushed into a ball by Tatsumaki. Gyoro Gyoro worried slightly about the S-Class' powers, especially Tatsumaki, but Orochi reassured Gyoro Gyoro that it will not be a problem as they can make as many Mysterious Beings as they please.

During the Council of Swordmasters meeting, called by Atomic Samurai, one of the Council members, Haragiri, transformed into a Mysterious Being by injecting himself with Monster Cells and ordered the others to do the same. Atomic Samurai rejected the offer and killed Haragiri. Through his robot, Metal Knight was able to spy on the discussion between Gyoro Gyoro and Orochi. When asked about their goals, Gyoro Gyoro simply tells him to watch and wait. At the hospital the Tank Topper Army fought the monsters and protected the patients and staff members. Mumen Rider struggled against Gyoffrey, but was saved by Tanktop Master.

Gouketsu and The Three Crows interrupted the closing ceremony of the Super Fight Martial Arts Tournament in an attempt to transform all of the martial artists into monsters. Gouketsu brought one Monster Cell for each martial artist. Rosie, Choze, Benpatsu, Hamukichi and Volten all joined the Monster Association, though Rosie was quickly killed by Choze. While the other martial artists were frightened, Suiryu decided to rebel against them. After Suiryu managed to defeat all of the martial artists, Gouketsu was impressed and offered Suiryu an executive position in the association. He was rejected and Gouketsu struck Suiryu down.

Gouketsu then toyed with Suiryu, stomping and punching the martial artist, giving him only three seconds to recover. In an attempt to win, Suiryu asks Bakuzan, the last standing martial artist for aid, but Bakuzan instead ate several monster cells and collapsed on the floor, seemingly dead. Gouketsu then ordered The Three Crows to finish off Suiryu, but the Crows were later killed by Suiryu in a team effort with Lightning Max and Sneck. After the Crows were killed, Gouketsu was challenged again by Sneck and Lightning Max. He easily defeated them and when Suiryu tried to leave the stadium, Bakuzan woke up from his transformation and blocked his entrance. Bakuzan then continuously stroke Suiryu on the ground.

Gyoro Gyoro used its spy drones to watch the chaos in the city and confirmed that their first objective was successful, as they also captured Waganma, the son of a Hero Association sponsor. Phoenix Man noted they lost many monsters and asked for reinforcements, but the request was denied. The monster noted that Nyan managed to recruit several new members and Gyoro Gyoro ordered Gouketsu to leave the stadium, but Gouketsu refuseed. Gouketsu questions Bakuzan and tells him to go with him to the Monster Association hideout. Bakuzan refused and fought Gouketsu. Gouketsu then warned Bakuzan about his attitude and informed him of Orochi, the strongest being on Earth. He gives Bakuzan a firm warning as he leaves the stadium for Z-City, the meeting point of the Monster Association.

As Gouketsu was heading towards the hideout, Saitama came and they fought off-screen, with Gouketsu's decapitated head comes flying into the stadium and lands in front of Suiryu. Free Hugger managed to injure Puri-Puri Prisoner, but the monster was squeezed to death by the hero.

Monster Association Arc
Elsewhere, Gale Wind and Hellfire Flame attacked Speed-o'-Sound Sonic who was training in the forest. As they were discussing, the ninjas revealed they have joined the Monster Organization and with their advanced training managed to retain their human form. Gale Wind and Hellfire Flame revealed they joined the Association to rule the world, more specifically to kill Flashy Flash and ask Sonic to join them. Sonic initially refused, but when Gale Wind demonstrated his speed after his transformation, Sonic was persuaded and took a Monster Cell. Later Sonic cooked the Monster Cell into a gourmet meal, however he didn't transform into a monster and had an upset stomach afterwards instead.

In W-City, Marshall Gorilla still wandered around the streets, feeling unsatisfied by his threat level being Tiger and wanted the Hero Association to change it to Demon. Zombieman was following the monster and wanted to gather as much information about the organization and its hideout. Marshall Gorilla then spots someone on the streets and was surprised to see Armored Gorilla, who was shopping for groceries. Marshall Gorilla felt angry that Armored Gorilla "sided" with the humans and attacked him only to be easily defeated.

In A-City, Destrochloridium took control of an association member and took one of Gyoro Gyoro's drones so they could declare war on them. He killed one of the association members before being killed by Superalloy Darkshine. In Z-City, Gyoro Gyoro gave a speech to the monsters and Orochi decided to eat Awakened Cockroach for failing to kill Genos. Orochi wanted to kill Do-S as well, but decided not to, since Gyoro Gyoro stated her powers were useful. When they noticed Gouketsu's absence, Gyoro Gyoro used one of its drones, only to find Goukestsu's headless corpse.

While Garou was being attacked by Genos, Bang and Bomb, some of the Monster Association's members arrived to save him, but were swiftly beaten. Phoenix Man swooped in and saved Garou and Elder Centipede caused mayhem.

Elder Centipede then attacked and overwhelmed Bang, Bomb and Genos, before being killed by Saitama. Meanwhile, Phoenix Man escaped with Garou. At the Monster Association base, Garou woke up and encountered Monster King Orochi, Gyoro Gyoro, Royal Ripper, Bug God, G5 and many other monsters. Garou was offered an executive position under the condition that Garou killed a hero within a day. He left to do so while being tailed by Royal Ripper and Bug God. After tailing him, Royal Ripper and Bug God deemed Garou to be unworthy and attacked him. Due to Sludge Jellyfish holding Tareo hostage, Garou was stabbed to the point of unconsciousness. Tareo was taken back to the Monster Association and thrown in the same cell as Waganma. Gyoro Gyoro reprimanded Royal Ripper as the Hero Association will attack soon and they need to be focused on the coming battle.

Various monsters such as Maiko Plasma and Electric Catfish Man were discussing their battle. Phoenix Man, after discussing Orochi's proccess of monsterization with Gyoro Gyoro, contemplated on becoming the Monster King. Do-S was training the mind controlled mercenary. Hellfire Flame and Gale Wind were training against each other. Pureblood drained another monster dry of blood for not walking out of his way. Devil Long Hair was talking with another monster while Pureblood looked on in disdain. Nyan was chatting with the monsterized prisoners from the Smelly Lid Prison. G5 collected Metal Knight's head and threw a monster at The Great Food Tub. Garou woke up from his injuries and headed towards the Monster Association base. Meanwhile, Child Emperor nearly finished the location the Monster Association base.

Garou killed any monsters he came across and saved Tareo from Royal Ripper by killing the monster. Garou ate a monster's arm to replenish his lost blood. They came across Overgrown Rover and quietly escaped only to run into Showerhead, Unihorn and Super Mouse. Garou fended them off but attracted Overgrown Rover's attention. The three monsters were killed by Overgrown Rover and Garou engaged it in battle. Garou was blasted to the floor Gyoro Gyoro resided. Garou was immoblized by Gyoro Gyoro psychic power. Gyoro Gyoro told Garou the secret of overcoming the Limiter by repeating experiencing death and overcoming it as was the case with Orochi. Gyoro Gyoro planed to use Garou to create the ultimate monster. Garou refused and planned to hunt Gyoro Gyoro and destroy the Monster Association. Orochi intervened and overwhelms Garou in their battle, knocking him out.

Later, the Hero raid on the Monster Association base takes place. Several monsters, including Evil Eye and Rhino Wrestler are sent to kill the invading heroes, but they are killed.

Flashy Flash encountered and killed Hellfire Flame and Gale Wind. Flashy Flash lost his Locator during the battle and followed a random path. Child Emperor found the decommissioned Metal Knight unit. He searched the robot's database and found the location to Waganma's cell. As he left, Child Emperor encountered Phoenix Man and shredded the monster. Child Emperor saved Waganma and the hero killed Sludge Jellyfish. While leaving they ran into G5 whom they retreated from. During their retreat, they came across Phoenix Man's corpse. Phoenix Man's resurrection activated and he returned fully healed and stronger with a disaster level of Dragon. Child Emperor was forced to summon his ace weapon, Brave Giant to battle. Their battle resumed with Phoenix Man getting stronger with each new resurrection. Phoenix Man revealed his new ability to resurrect the dead to fight and brought back the Subterranean People, Gale Wind and Hellfire Flame to fight. While the Subterranean People were incinerated, Gale Wind and Hellfire Flame were brought back to life after being electrified by Brave Giant. Child Emperor defeated Phoenix Man by sneaking Tickle-Tickle Bug 1 into his suit and causing the monster to rip apart his costume. With his powers lost, Child Emperor ended Phoenix Man.

Zombieman was killing any monsters he encountered and was led to Pureblood. After a grueling 30 minutes, Pureblood laid defeated. After defeating the remaining monsters, Zombieman left to carry on his mission. Pig God encountered and devoured The Great Food Tub. The Disciples of Atomic Samurai encountered Do-S and the mind controlled Narinki's Private Squad. Their battle was interrupted by Sweet Mask who took control of the battle and told the swordsmen to leave. As they left, they encountered Pig God in the middle of digesting The Great Food Tub and decided to take another route. The swordsmen encountered Devil Long Hair and they battled.

Meanwhile Puri-Puri Prisoner was battling some monsters. Puri-Puri Prisoner encountered the demon-level monster Vacuuma who could absorb monsters and use their powers. Despite this ability, the hero defeated the monster. The Smelly Lid Prisoners who were monsterfied confronted Puri-Puri Prisoner to kill him but the hero mistakenly believed they were bewitched by the Monster Association. Nyan attacked Puri-Puri Prisoner but wass put off by his strange personality and opted to run away. Puri-Puri Prisoner gave chase and accidentally killed almost all of his fellow inmates.

Superalloy Darkshine was in battle with Bug God, resisting every of the monster's attacks without retaliating. When Bug God mocked Superalloy Darkshine for this, the hero counters by stating the monster fell below his expectations, and adds that he, Tatsumaki, and King are not to be angered. Bug God, offended by this, eventually assumes a more powerful form and attempts to defeat the hero, only to be crushed by a single of his attacks.

Meanwhile, Saitama encountered Overgrown rover and easily fended the monster's blast and sent it flying with a single punch, causing a loud tremble that went noticed by the heroes and the excecutives alike. Nyan, shocked by this, attempts to sneak attack Saitama, only for his attack to have no effect. Realizing the risk of fighting Saitama, Nyan quickly retreats.

In another place of the headquarters, Tatsumaki encountered Gyoro Gyoro, who boasted the organization's goal to create a world of monsters and engaged her in combat, first by trying to overpower her by crushing her in compacted debris, to no avail. Tatsumaki ripped a chunk of Gyoro Gyoro's body with a single psychic blast, prompting the monster esper to assume a more powerful form and trying to pin her with 300-fold gravity, which proved to be in vain as Tatsumaki ripped Gyoro Gyoro's body, and realized said body was a meat puppet. Desperate, Gyoro Gyoro pleaded to Orochi for help, only to her cry for help to go unheard as Orochi's attention was diverted to Saitama.

Orochi mocked Saitama and tried to attack him, only for his blow to be intercepted, and for him to finally realize the previous impact was Saitama's doing and recognizing him as a dangerous threat to be eliminated. Saitama crushed one of Orochi's appendages and later easily dodged one of his fire blasts. As Overgrown Rover was nearby recovering from the previous impact, Orochi commanded him to kill Saitama, only for the canine monster to flee in fear upon recognized who overpowered it. As Saitama effectively admitted he beat up Overgrown Rover, Orochi inmediately realized he was behind Gouketsu and Elder Centipede's deaths, and feeling a long-unfelt excitement, Orochi unleashed all his power on Saitama, while boasting about it, which annoyed Saitama. The ensuing battle's ripples were felt throughout the heatquarters and the entirety of Z-city, as Atomic Samurai fended one of Orochi's astray blasts, Fubuki and his group to guard from another, the city landscape to be leveled, and a large subterranean area to be pierced in a clean line from another blast. Saitama easily rushed towards Orochi and killed him with a single normal punch. As he died, Orochi wondered about feeling terror for the first time.

Gyoro Gyoro, through one of her drones, found Orochi dead and tried to find the one responsible in order to devise countermeasures, only for her drone to be crushed by Saitama. Tatsumaki finishes what is left of Gyoro Gyoro's body, only for a a humanoid figure to emerge from its remains, who Tatsumaki recognized.

Elsewhere, a monster posing as Waganma tried to fool a fearful King into following him to a trap, only to melt in fear itself upon mistaking King's meek stance as an intimidating stance.

The battle between Iaian, Okamaitachi, Bushidrill, and Devil Long Hair eventually ended as the monster's weak point, his hair, was cut short. Elsewhere, Atomic Samurai easily cut through monsters and eventually encountered Sword Devil Excecutioner, whose blows were easily blocked by the hero and easily fell to him. G5 engaged Atomic Samurai after collecting data in order to copy his abilities. Despite being initially evenly matched, Atomic Samurai cut through G5, though the robotic monster's core was intact and eventually escaped. As Black Sperm was chasing Tareo, he encountered Atomic Samurai.

After Saitama defeats Garou, the organization collapses. Psykos is taken prisoner. Homeless Emperor is killed by "God". Pig God digests Evil Natural Water. So far, Black Sperm and Black Rover, who are currently living as Saitama's pets, are the only surviving members of the organization.

Members
Upper Echelon= Regular Members= {|style="margin:auto;" width="76%" ! colspan="4" style="background-color:black; color:#ffffff; font-size:110%;" | Unknown Evil Eye.png Gyoffrey Profile.png Haragiri.png Junior Centipede.png Sword_Devil_Executioner.png Human Bird Grass Profile.png }} Recruits=
 * Evil Eggs.png
 * Evil Eggs.png

* There are also numerous unnamed regular members.

Webcomic and Manga Differences

 * The Monster Association is expanded upon in the manga, having more members and having them come out to the public. In the original web-comic, it only had 17 members: Black Sperm, Bug God, Devil Long Hair, Evil Natural Water, Fuhrer Ugly, Gale and Hellfire, Goddess Glasses, Gums, Homeless Emperor, Overgrown Rover, Phoenix Man, Psykos, Pureblood, Royal Ripper, Senior Centipede and The Great Food Tub. In the manga, however, they have around 500 members.
 * All of the members in the web-comic are Demon or above.
 * The leader is Psykos, as Orochi does not exist in the webcomic.
 * Monster Cells were introduced in the manga, and never existed in the web-comic.
 * In the manga-only, The Organization sent G5 to assist the Monster Association, tying the two factions together.

Trivia

 * The idea of the Monster Association being previously the home of the Subterranean People was a suggestion by a fan on stream.
 * In both the web-comic and the manga, the Monster Association mirrors the Hero Association.
 * In the web-comic, the Monster Association has 17 members, which is the number of S-Class heroes in the Hero Association.
 * In the manga, the Monster Association has around 500 members, which is roughly the number of pro heroes in the Hero Association.
 * Monsters who are not a part of the Monster Association are sometimes referred to as freelance monsters by members of the association.