Jounouchi Hisashi is a high school student whose life is defined by a profound and unresolved internal conflict between a childhood dream of heroism and a deep-seated personal cowardice. As a young boy, he harbored a strong desire to be a hero, a figure of strength admired for great and courageous deeds. This ambition was shattered by the discovery of a bone tumor, a condition that permanently prevented him from ever achieving peak physical condition. Faced with this limitation, his inherent fear of death and hardship led him to abandon his aspirations entirely, convincing himself that his body was now an insurmountable barrier to becoming the person he wanted to be.

His personality is primarily shaped by this cowardice. He is not motivated by a genuine messianic complex or a selfless desire to save the world. Instead, his actions are a method of self-validation. Helping others allows him to perceive them as weak and himself as the sole individual with the strength to rescue them, a dynamic that bolstered his own fragile ego. This internal struggle was crystallized during a formative encounter in a hospital, where he overheard a conversation between a detective and a young girl named Nagi Kirima. When the detective expressed a wish to be a defender of justice free from rules, Nagi replied that he could probably do it if he tried. For Jounouchi, who felt permanently stuck in a rut, this simple assertion of unlimited potential only deepened his despair over his own perceived inability to act.

Jounouchi's life is dramatically altered on the night a mysterious pillar of light illuminates the city. After this event, he awakens to a strange new ability: he can see large, spider-like insects clinging to the chests of the people around him. He soon discovers that these insects represent emotional knots, personal worries, painful memories, and deep-seated sorrows. His initial instinct is to remove these insects by grabbing and physically devouring them, a grotesque act that he believes liberates the afflicted person from their distress. This newfound power provides him with the opportunity he always wanted. He immediately embraces the role of a savior, feeling a powerful sense of accomplishment and heroism as he goes on a spree, clearing the spiders from his classmates, his father, and others.

However, this ability is not a pure blessing but a deeply flawed and destructive power. When he removes a spider from his father in an attempt to ease the pain of losing his wife to a serial killer, the result is catastrophic. Instead of simply removing the sorrow, the act erases the memory of his mother entirely, leaving his father staring blankly at her photograph with no recognition. Similarly, a classmate he had "helped" to stop cheating is soon seen cheating again. Jounouchi learns that he is not healing people but consuming their memories, robbing them of crucial parts of their identity and history. Despite this horrifying realization, he is unable to stop. His craving for the feeling of being a hero has turned into an addiction, and he begins to justify his actions with the rationalization that it is better for bad memories to be forgotten. His heroism becomes a self-serving delusion, and other characters observe that his expression while consuming the spiders appears evil and sadistic, a stark contrast to the peaceful state of his dazed victims.

His primary role in the story is as the focus of the second episode, serving as a case study in how the strange phenomena in the city can corrupt a vulnerable individual. His tragic arc illustrates the dangers of unchecked desire and the perversion of a noble ideal. His key relationships are brief but pivotal. His encounter with Nagi Kirima as a child haunts him, representing the ideal of fearless resolve that he feels he can never attain. Near the end of his journey, she confronts the entity chasing him, instantly recognizing that it is not the true Boogiepop but a different force, further highlighting Jounouchi's entanglement in events beyond his comprehension.

In his development, Jounouchi begins as a conflicted but generally harmless coward. The acquisition of his power initially seems to fulfill his dreams, but it quickly reveals his selfishness and weakness. As he becomes addicted to consuming the spiders, he progressively loses his grip on morality and reality, transforming from a delusional helper into a desperate addict whose actions cause genuine harm. His final encounter is with a shadowy entity known as Boogiepop Phantom. As he flees in terror, his cowardice overtakes him completely. When the entity catches him, he does not destroy him but instead offers to "take him there." Jounouchi subsequently becomes one of the many students who have mysteriously disappeared from the city. His notable ability is the power to perceive and physically extract these psychic parasites from others, an act that consumes the targeted memories and emotions. This power is not a skill he controls but a compulsive, addictive behavior that ultimately leads to his own undoing.