Gyoro Gyoro is a major antagonist in the One Punch Man series, distinguished by its role as the strategic mastermind behind the Monster Association. At its core, Gyoro Gyoro is not an independent, living being but a construct, referred to as a meat puppet. This puppet is controlled remotely by the true leader of the Monster Association, a powerful esper named Psykos, using her psychic abilities from a hidden location deep underground. The puppet was created specifically to allow Psykos to manage the organization's operations without ever revealing her true identity or putting herself in danger. Only the Monster King, Orochi, was aware of the puppet's true nature and its connection to Psykos.

In terms of appearance, Gyoro Gyoro is a large, grotesque creature resembling a slug with a single, prominent eye, which is depicted as blue in the anime and red in the manga. Its body is fat and circular, with eight arms protruding from its head, four main arms, stubby legs, and three-toed feet. Its body color also varies between adaptations, appearing pink in the anime and green in the manga. When pushed into a serious confrontation, as seen during its fight with the hero Tatsumaki, Gyoro Gyoro can transform into a more powerful state where its skin darkens and numerous additional eyes appear all over its body. Despite its large size, towering over humans and smaller monsters, it is still dwarfed by giants like Orochi.

As a puppet, Gyoro Gyoro has no personality of its own, serving as a direct extension of Psykos's will. The personality it displays is therefore a reflection of Psykos herself, who is shown to be serious, cunning, and deeply committed to her duties. Gyoro Gyoro is often depicted as a calm and logical leader, acting as the primary strategist and advisor to Orochi. It treats other monsters as assets to be managed, valued for their utility. For instance, it requested Orochi spare the monster Do-S because her unique abilities would be useful in the future, and it disapproved of Royal Ripper playing with a hostage instead of focusing on the mission. However, it also has a low tolerance for failure and a sadistic sense of humor, as demonstrated when it falsely offered the Hero Association a chance for peaceful coexistence, only to treat the proposition as a joke before declaring war.

The primary motivation behind Gyoro Gyoro's actions is the complete domination and destruction of the Hero Association and the establishment of a world ruled by monsters. To this end, it orchestrates the Monster Association's military strategy, manages its executive members, and oversees key operations. A central part of its plan involves the creation of powerful monsters. Gyoro Gyoro is a scientist of monstrosity, having experimented extensively to discover the secret of breaking a being's limiter to make them explosively powerful. Its greatest success is Orochi himself, a human who was transformed into the ultimate monster through a brutal process involving cannibalism, torture, and other horrific experiments. Recognizing the same potential in the Hero Hunter Garou, Gyoro Gyoro becomes intensely interested in him, devising trials to push Garou to his limits in an attempt to cultivate him into a second Orochi and a powerful weapon for the Monster Association.

Within the story, Gyoro Gyoro serves as the primary antagonist commander during the Monster Association arc. It delivers the declaration of war to the Hero Association, gives speeches to rally the monsters, and personally assigns tasks to its powerful executives, such as Gouketsu, Elder Centipede, and Phoenix Man. Its key relationships are almost entirely utilitarian. It is the direct advisor to Orochi, who refers to the Monster King with respect as "Your Majesty". With other monsters like Phoenix Man, Gyoro Gyoro shares a relationship of mutual respect, as both are strategic thinkers, and it often explains its tactical reasoning to him. Its relationship with the hero Garou is that of an interested scientist and potential creator, seeking to break and remake him into a monster.

Gyoro Gyoro possesses a wide array of powerful abilities, which are actually the psychic powers of its unseen master, Psykos. Its primary ability is powerful psychokinesis, allowing it to move objects with its mind, create barriers, and manipulate gravity. It can increase the gravity around a target by hundreds of times, as demonstrated when it subjected Tatsumaki to three hundred times normal gravity. It can also use telepathy to communicate with others over long distances and deploy small spy drones shaped in its own image to gather intelligence remotely. Furthermore, it has the ability to sense the biological signals of anyone within the Monster Association's underground headquarters. A notable weakness of its psychic power is that it cannot effectively multitask, limiting its ability to maintain a psychic hold on a target while simultaneously performing other actions.

The development of Gyoro Gyoro as a character culminates in its destruction. During the Monster Association's invasion, it confronts the S-Class hero Tatsumaki. Initially confident in its power, Gyoro Gyoro transforms into its true form and unleashes its full might, but is utterly outmatched. Tatsumaki effortlessly tears the puppet apart, revealing that the entity is a mere meat puppet. Gyoro Gyoro cries out for Orochi to save it, but the Monster King is unable to come to its aid. Its final act is to send a spy drone to investigate what happened to Orochi, which is quickly destroyed. Gyoro Gyoro is ultimately dismantled by Tatsumaki, who then uses her powers to force the real body of Psykos out of hiding from far below the surface to finish the fight. With the puppet's destruction, the strategic head of the Monster Association is decapitated, exposing the true leader and leaving the organization in chaos.