Waganma strongly resembles his father, having large lips and short light-colored hair with sideburns that curl inward. His formal attire consists of a light-colored business suit and a polka dot bow tie.
Waganma is a curious child willing to try commoners sushi, but doesn't understand the etiquette of dining. He has faith that the heroes will rescue him when he was kidnapped. He is shown to be quite bratty, self-centred & manipulative, as he is willing to let Tareo be saved only if he follows his orders. He also displays immense cowardice, irresponsibility, and weak-willed behavior, as he let his fellow prisoner be taken by Royal Ripper at a moment's notice, then selfishly pretends he was the only captive when asked by Child Emperor if there were more hostages. Additionally, he recoiled into simpering obedience at Child Emperor’s brutality, despite Waganma's whiny and pampered attitude. Waganma also shows a hideously inflated sense of self-worth, often taking pleasure in bullying monster suppressed by the lower-ranked heroes while bragging about the Association. He also likes to make himself feel superior, as seen when he is trying to stomp on Monster Chick Man, it's clear he likes to pick on people smaller and weaker than him.
Waganma and his father Narinki eat at a cheap sushi restaurant with Metal Bat, who is assigned their bodyguard. Waganma, unfamiliar with the rules of the restaurant, keeps returning his finished plates to the conveyor belt, much to the annoyance of Metal Bat. Suddenly, Junior Centipede and Venus Mantrap appear and grab Waganma.
Metal Bat quickly frees Waganma and defeats the monsters. They are then attacked by Senior Centipede and Rafflesidon. Rafflesidon immobilizes Waganma and Narinki with a gas attack. Metal Bat defeats the monsters after a brief fight and orders Pineapple and Mohican to take Waganma and Narinki to the hospital. They are unable to get far because of Elder Centipede, who emerges from the ground to kidnap Waganma. Metal Knight makes a sudden appearance and attacks the monster with his weapons, drawing its attention from the heroes on the ground. The heroes continue to run, but their progress is halted by Rhino Wrestler, Phoenix Man, and Sludge Jellyfish. Rhino Wrestler defeats the two heroes and the monsters take Waganma and retreat underground.
Waganma is later seen tied up in chains in the Monster Association headquarters, as a hostage.
Royal Ripper brings Tareo into Waganma's prison cell. Waganma mentions that he was captured the day before and that he was fed only bread and water. He expresses his hunger and quickly snatches a candy from Tareo and asks if he has any more food. Waganma comments on Tareo's uselessness and the monster's stupidity for capturing him as his father is an important figure to the Hero Association. Waganma tells Tareo that the heroes will come to save them, though mentioning that his safety comes first. He recruits Tareo as his lackey in exchange for all the food Tareo receives.
Sludge Jellyfish goes to the cell where Tareo and Waganma are being held, and tells them there is no hope for either of them to be saved. Waganma disagrees, and says the Hero Association has plenty of heroes and goes off to list the names of several heroes, such as Metal Bat and King. At the mention of King's name, Sludge Jellyfish becomes frightened but confidently states the whole purpose of the Monster Association is to eliminate such heroes and goes on to mention the Executive Members of the Monster Association, speaking in awe of their strength and remarking they must have been created by God. He states that there is no way humanity can win and that even King will fall.
Waganma is saved by Child Emperor, who takes out the guards with poison gas. He whines at the hero's tardiness but quickly apologizes after seeing Child Emperor's stern look. They come across G5 who easily resists Child Emperor's initial attacks. The hero instructs Wagnma to get behind him. Child Emperor distracts G5 with Mad Dog Underdog Cerberus and flees with Waganma. Waganma asks Child Emperor why he didn't help his robot battle G5. The hero replies that the safety of Waganma is their top priority, to which Waganma hastily agrees.
They come across the body of Phoenix Man, whom Child Emperor had defeated earlier, and Waganma recognizes the monster from the black comedy TV show, Animal Kingdom. He explains that the character, Birdbrain, would often be killed through his stupidity but revive the next episode as if nothing happened. Suddenly, a bright light flashes behind Waganma and Resurrected Phoenix Man appears. The monster sends searing hot winds at them and Child Emperor protects Waganma with his umbrella projecting shield. The hero leaves him there to confront the monster.
Child Emperor is forced to summon his ace, Brave Giant, and do battle against Phoenix Man. During their battle, the two heroes Child Emperor and Saitama protect Waganma from further danger. After Child Emperor's victory against Phoenix Man, his Underdog Man robot arrives, taking Waganma and the two heroes up to the surface along with the captured criminals Gale Wind and Hellfire Flame. When asked by Child Emperor if he saw anyone else down there, Waganma lies and says he is the only hostage. They leave the scene and make their way to the surface. Child Emperor passes Waganma to the support team and makes his way back into the Monster Association base to rescue Tareo.
With the hostage secured, the support team attempts to return Waganma to safety, but their progress is halted by Nyan, who quickly incapacitates several of the heroes. Nyan recognizes Waganma as the child the Monster Association had taken hostage. Sekingar, sensing Nyan's murderous intent towards Waganma, instructs Food Battler Futoshi to return to the Hero Association headquarters with the child. After defeating the rest of the heroes, Nyan turns his attention to the fleeing Waganma, who urges Futoshi to pick up the pace.
Waganma gloats in the heroes' apparent victory after Gearsper buries Nyan in the rubble. His excitement is short-lived as Nyan quickly escapes from the pile and drags him away to kill him. Nyan's grip on the boy is suddenly cut off by a high-speed projectile, which turns out to be the shape-changing box of Drive Knight. Waganma runs away with Food Battler Futoshi and taunts the monster's apparent misfortune of encountering the S-Class hero.
Eventually, Futoshi begins to run out of calories and slows down considerably, much to Waganma's annoyance. However, Genos suddenly appears from behind them and scoops them up, quickly carrying them and the rest of the defeated support heroes out of Z-City. They reach a Monster Association military convoy, where Waganma demands that Genos stay with him to protect him. However, Futoshi offers to take his place, believing that Genos is much better suited to go help the other heroes in the Monster Association raid.
- "Waganma" is a play of words of "Wagamama" (我が儘) which means "selfish".