Gang Wooju, originally named Fuyuki Hinata, is a central figure in his story. He is a young teenager, typically depicted as being in the first year of middle school, around thirteen years old. He has a slim build and stands at an average height, with dark blue or black hair that has a pointed tuft at the back and dark blue eyes. His name carries the meaning winter tree, which contrasts symbolically with his sister, whose name means summer beauty.

Fuyuki’s most defining characteristic is his deep and passionate fascination with the occult, paranormal, and supernatural phenomena. He has a strong interest in unidentified flying objects, ghosts, cryptids, ancient civilizations, and mysterious creatures from beyond Earth. This curiosity is so central to his identity that he establishes an Occult Research Club at his school to explore these topics with like-minded peers. Despite his enthusiasm, he approaches even his favorite subjects with a rational and often skeptical mind, questioning dubious claims and seeking logical explanations, though he remains open to wondrous possibilities.

In terms of personality, Fuyuki is generally calm, reserved, polite, and compassionate. He is forgiving to a fault and tends to avoid conflict and physical confrontation. This gentle nature is most visible in his interactions with others, as he treats everyone without prejudice. However, his patience is not infinite. When pushed past his limits by the thoughtless or dangerous actions of those close to him, Fuyuki is capable of an intense, terrifying rage. The full expression of his anger is so fearsome that the narrative famously never shows his face when he is truly furious, only the horrified reactions of those around him, including his far more athletic and combative sister. This hidden temper underscores a deeper inner strength that lies beneath his unassuming exterior.

His motivations are driven by a desire for friendship and understanding rather than conquest or heroism. He dreams of encountering and connecting with the unknown, a wish that is granted when he discovers an alien frog named Keroro hiding in his home. Rather than fearing the invader, Fuyuki is thrilled and quickly befriends him, cementing the alien's stay in the human household. This relationship forms the core of his role in the story. While Keroro and his platoon continuously devise plans for world domination, Fuyuki acts as a steadying moral influence and a voice of reason. He often thwarts their schemes not through force, but by appealing to the friendship they share, asking, Arent we friends? to deter the frogs from their most destructive plans. His open-mindedness and kindness also make him an accidental diplomat, having successfully calmed hostile aliens and prevented the Earth's destruction on multiple occasions through empathy and persuasive words rather than violence. This has led to him being informally recognized as a space diplomat.

Fuyuki's key relationships shape much of his daily life. His bond with Keroro is brotherly and close, with Fuyuki being endlessly curious about the alien's technology and culture while Keroro enjoys his company and shared hobbies like video games. He lives with his mother, Aki, and his older sister, Natsumi. Unlike his athletic and physically powerful sister, who is often the first to fight the alien invaders, Fuyuki is the families emotional center and a foil to her hot-headedness. At school, he is the object of affection for the wealthy classmate Momoka Nishizawa, though he remains largely oblivious to her romantic advances, viewing her as a good friend. He also forms a unique connection with the alien hunter Alisa Southerncross, whom he forgives for initially hostile actions and hopes to befriend, demonstrating his limitless capacity for understanding.

Throughout the story, Fuyuki shows subtle development. While he begins as a passive enthusiast of the unknown who is physically weak and dislikes exercise, especially swimming, his experiences expand his world considerably. He faces genuine dangers and takes on significant responsibilities, actively working to protect the Earth through non-violent means. His competence in these high-stakes situations reveals that his calm demeanor can become a source of great strength in a crisis, proving to be more resilient than his sister when faced with overwhelming psychological pressure.

Besides his skills in diplomacy and storytelling, Fuyuki possesses a few notable if unorthodox abilities. He is an exceptional teller of scary stories, capable of turning mundane tales into genuinely frightening experiences with his atmospheric delivery and eloquence. He also exhibits a hidden talent for bowling, a sport in which he excels to the point of surpassing his naturally athletic sister. His primary strength, however, remains his boundless empathy, his ability to connect with beings from all walks of the universe, and his surprising inner resolve that manifests when his friends and the world are in genuine peril.