Overgrown Rover

Overgrown Rover (育ちすぎたポチ, Sodachisugita Pochi; Viz: Overgrown Pochi), also called Rover, is a Dragon-level Mysterious Being and an executive member of the Monster Association. Its role is to guard the Monster Association headquarters.

After the Monster Association's downfall, he becomes Saitama's pet alongside Black Sperm and is currently entrusted with Forte, Chain'n'toad, and Butterfly DX.

Appearance
Rover is a very large, black, six-eyed dog monster. Its eyes are ruby colored. It has very large fangs and four toes per paw. Its fur is very roughed up. It lacks a tongue.

After the battle between the Hero Association and the Monster Association, Rover shrinks to the size of a puppy.

Personality
Rover behaves like a dog. It is a diligent and loyal guard dog, instantly tracking down Garou after the Hero Hunter helped Tareo escape and did not stop under any circumstances. However, under intense and traumatic conditioning, it was forced to learn to sit even if the command was given by an enemy

Rover, however, does not instantly grow hostile toward intruders, as he neither attacked nor followed Garou and Tareo in his initial encounter with the pair, leaving them alone when they backed off slowly. Additionally, Rover does not seem to differentiate from friend or foe when angered, as he attacked and killed fellow monster Unihorn after the latter accidentally hit Rover during a fight with Garou.

Rover's canine behavior also means that he can be trained by someone, though they must have enough physical strength. Garou jokingly tells him to sit during their battle before striking him to no effect; however, Saitama did the same and successfully conditioned Rover into obeying the command to "sit", which Bang unintentionally exploited later. He also came to fear Saitama because of this encounter, and disobeyed Orochi's commands and fled instead.

Monster Association Arc
Overgrown Rover encounters Garou and Tareo when the two are trying to escape the Monster Association Headquarters.

After Garou and Tareo slowly walk away from Overgrown Rover, three other Demon level monsters, Super Mouse, Showerhead and Unihorn appear and fight Garou. Unihorn uses his Trinity Demon Bursting Speed Thrust and launches itself at Garou. Garou brushes him off, and he shoots into the distance. Garou takes a moment to realize that that was where Overgrown Rover was, and hears its roar. Unihorn's head is then thrown back all broken up. After a moment, Rover finally joins in the battle and fires an energy blast from his mouth. Garou grabs Tareo and narrowly outruns the energy blast. Once Garou makes it to the surface, he tells Tareo to run while he handles Rover. Garou strikes Rover's front left leg in an attempt to throw him off balance, but Rover merely shrugs it off and fires another energy blast. This time, Garou is unable to escape it and is forced to take the full brunt of the blast, which destroys several floors of the Monster Association headquarters in the process. When Rover sees Garou standing, he fires a rapid barrage of energy blasts as he runs across the walls. This time, Garou manages to avoid all of the attacks, and strikes a powerful blow on Rover's forehead. However, Rover merely shakes off the attack and comes out completely unharmed, shocking Garou. Rover then bites down on Garou's leg and shakes him around like a rag doll before shooting another point-blank energy blast at Garou, which destroys several more floors of the headquarters. Afterward, Rover stops pursuing Garou and allows Psykos to finish Garou off. While Saitama is roaming the Monster Association headquarters, Rover encounters Saitama. Rover growls angrily at Saitama, then fires an energy beam at him. Saitama jumps over the beam, calling Rover a "bad dog" and remarking at his lack of training. Saitama tells Rover to sit and punches Rover into submission.

When Saitama meets Orochi, and during the ensuing battle, Rover wakes up. Orochi notices Overgrown Rover is still alive and orders Rover to attack Saitama. The monstrous canine looks at Saitama, but upon seeing him, he recognizes him and immediately retreats in terror, surprising Orochi and prompting him to ask Saitama what he did to Rover. Saitama simply tells Orochi that he gave Overgrown Rover a beating, and the two resume their battle. Later, Rover encounters Bang, Bomb, and Fubuki and fires energy blasts at them. Despite his injuries from Saitama, Overgrown Rover continues to pursue and attack the three intruders with his lethal energy blasts. Bang and Bomb deflect the monster's attack and hit Overgrown Rover with their combination attack Cross Fang Dragon Slayer Fist. Despite their best efforts, Rover still survives their onslaught. Out of annoyance, Bang rhetorically asks why Rover couldn't simply be quiet and sit down. Rover, remembering being forced into submission by Saitama after he gave the same command and being overpowered by both martial artists, obediently sat and stopped the fighting.

For the remainder of the invasion, Rover's enormous size begins to reduce drastically until it became no bigger than an average dog due to the damage he took from his multiple battles.

Psychic Sisters Arc
After the destruction of the Monster Association, Rover encounters Saitama again, but instead of killing the former monster he merely lifted it, mistaking it for a lost dog. Black Sperm, watching them, then decides to follow Saitama as well, thinking that his chances to survive were bigger with him, and together, he and Rover persuade Saitama to take them to the Hero Association's headquarters in A-City, which the hero only begrudgingly accepts.

At the entrance, however, the security system recognizes Rover and Black Sperm as monsters and sends defensive robots to deal with them. Black Sperm hides behind Rover, who growls at the robots and they then witness Saitama destroying all of the robots. When staff members of the association asked Saitama about the event, Black Sperm was hiding in Rover's stomach. Rover and Black Sperm are later entrusted to Butterfly DX, Chain'n'toad, and Forte after the latter lost a bet with Saitama after he got hit by a car. Even though the heroes protested at first, after Forte finally witnessed Saitama's true strength, he accepted responsibility over them with his compatriots and advised them to work on being accepted by Saitama as well. Forte is later seen building a dog house for Saitama's new pets.

Ninjas Arc
Genos takes Rover for a walk outside.

Abilities and Powers
As a high-ranked member and a Dragon-level Mysterious Being of the Monster Association, Overgrown Rover is an extremely powerful being, and quite possibly one of the most powerful Dragon-level mysterious beings to date. During his battle with Garou, he effortlessly tanked several blows from him and held the advantage for the entire match. Additionally, both Gyoro Gyoro and Orochi were in shock and disbelief that Overgrown Rover was not only defeated, but fled when given an order to attack Saitama, showing that defeating such a monster, even in the eyes of the leaders of the Monster Association, is extremely difficult.

Supernatural Abilities
Energy Projection: Rover is capable of firing destructive energy bursts in rapid succession from his mouth. These energy blasts are powerful enough to incinerate stone, level city blocks, and destroy several floors of the Monster Association Headquarters with ease along with severely injuring Garou and killing two Demon-level beings in a single shot. Rover's energy blasts can also cause shock waves strong enough to shake the surrounding surface area of Z-City that Saitama mistook as an earthquake. While the projectiles are presumably energy balls, Saitama noted it to be "fire".
 * Trajectory Bending: Rover can change the trajectory of his energy balls, causing them to chase after their targets.

Physical Abilities
Immense Strength: As a Dragon-level monster, Rover boasts a tremendous amount of strength and power. He was able to slam Garou against the wall and floor with ease and break Unihorn, a monster that boasted a nigh-unbreakable horn.

Immense Durability: Rover is incredibly durable, being able to withstand hits from Bang, Bomb, Garou, and even Saitama without receiving any or little damage, a very impressive if not nearly impossible feat to accomplish, although Saitama admitted he was going easy on Overgrown Rover. Rover also forced Bang and Bomb to use Cross Fang Dragon Slayer Fist, a technique more powerful than the one used on Elder Centipede.

Immense Speed: Rover is quite fast and able to keep up with S-Class heroes such as Bang and Genos. He was also able to outpace Garou and was fast enough to run horizontally across the wall of the Monster Association Headquarters.

Enhanced Stealth: Despite his enormous size, Rover is stealthy enough to appear behind Garou and Tareo without either of them noticing until Garou turned around.

Fighting Style
Rover has no refined fighting style; his attacks are limited to bombarding his enemies with energy blasts or biting and shaking them like a dog. Whenever an enemy enters his domain with hostile intent, Rover relentlessly attacks until the target escapes or dies.

Guard Dog: Due to his canine nature, Rover is assigned to guard the entrances of the Monster Association against intruders.

Trivia

 * Effectively, Rover's Japanese name "Pochi" is a common name for dogs in Japan, similar to "Rover". Moreover, this name is similar to poochy, that refers to the disproportionate size of Overgrown Rover.
 * Murata has shown Rover's design on a wedding card before the monster's manga debut.
 * In the webcomic, Garou and Rover begin to fight without encountering Unihorn, Showerhead and Super Mouse. Garou puts a much better showing and ends up telling Rover to sit. Garou punches Rover into the ground where they were fighting, leading them to fall into the headquarters' basement.


 * Rover is the second mysterious being to survive a punch from Saitama, the other 4 being Boros, Orochi, Awakened Garou, and Evil Natural Water. Though in Rover's case, Saitama was holding back and had no intention of killing him.

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