Hoyuelos is introduced in Mob Psycho 100 as a powerful and malicious high-level spirit, characterized notably by the circular blush or dimple marks on his cheeks. His initial plan involves establishing a religion or cult called "LOL" with the ambitious goal of gaining followers and ascending to become a god worshipped by people. During this time, he encounters Shigeo Kageyama, better known as Mob, and attempts to make the emotionless boy laugh, facing him in a staring contest which ultimately fails. Following a confrontation where Mob defeats him, Hoyuelos does not get fully exorcised. Instead, his power is significantly reduced, and he is transformed into a small, nebulous green spirit who begins following Mob around constantly.

In this diminished state, Hoyuelos initially has ulterior motives; he follows Mob with the clear intention of eventually gaining his trust and possessing his powerful body. Despite these self-serving beginnings, his constant proximity to Mob leads to an unexpected dynamic. Hoyuelos develops a personality that contrasts sharply with Mob's sincere and straightforward nature, often acting as a cynical, street-smart, and pragmatic advisor or voice of reason. Although he cannot resist making snide comments or looking out for his own interests, he gradually becomes attached to the boy and finds himself incapable of truly harming him. This ambiguous status sees him operating almost as an unofficial companion or mascot, hanging around Mob's shoulder and interacting with other characters like Arataka Reigen, for whom he often expresses disdain but ultimately cooperates with to a certain extent.

A significant turning point in Hoyuelos's development occurs much later when he once again sees an opportunity to gain divine power. He takes control of a massive, unnatural broccoli known as the Divine Tree that has sprouted in the city, using the faith of its worshippers to become the powerful entity known as the Psycho Helmet. This betrayal leads to a final and serious battle with Mob. In the end, Hoyuelos is defeated again, leading to a moment of genuine emotional impact where he seemingly disappears, causing Mob to cry. Despite his constant scheming, underhanded personality, and initial malice, Hoyuelos serves as an unlikely and complex figure in Mob's life, representing a being who is neither fully evil nor truly heroic, capable of both selfish ambition and reluctant companionship.