Fuyuki Hinata is a central human character in the story, a middle school boy typically around twelve to thirteen years old. He lives in the Hinata household with his mother, Aki, and his older sister, Natsumi. He has black hair and violet or blue eyes, and is often depicted wearing a blue hoodie. Fuyuki’s defining characteristic is his deep and enthusiastic fascination with the paranormal and the occult, encompassing everything from ghosts and urban legends to UFOs and ancient mysteries like Stonehenge or the Bermuda Triangle. This passion is so strong that he founds an Occult Research Club at his school, though it only has a few members.

In personality, Fuyuki is generally kind, polite, and relaxed, especially when compared to his more aggressive and athletic sister. He is naturally curious and open-minded, a trait that initially makes him excited rather than frightened by the arrival of the alien Keroro platoon in his home. Despite his fascination with the unknown, he paradoxically lacks any real spiritual sensitivity or psychic ability, which contrasts with his sister Natsumi, who does possess such instincts. He is also noted for having very poor stamina and a strong dislike for physical exercise and sports, viewing them as his worst fear. This physical weakness is a source of comedy, especially in contrast to Natsumi’s athletic prowess. However, Fuyuki has a hidden side; on the rare occasions when he becomes genuinely angry, his demeanor becomes terrifying enough to frighten even his sister and the entire Keroro platoon. He is also known as a masterful teller of horror stories, able to use his atmosphere and eloquence to make even mundane tales frightening.

Fuyuki's primary role in the story is as the closest human companion and partner to Sergeant Keroro, the leader of the alien invasion force. He is the first to discover Keroro and insists on befriending him, much to Natsumi’s initial dismay. Rather than being a fighter, Fuyuki often serves as a diplomat and a moral compass for the platoon. He consistently refers to Keroro with the respectful title gunso, meaning sergeant, reinforcing their unique dynamic. While Keroro is obsessed with mundane Earth hobbies like building Gundam models, Fuyuki is drawn to the extraordinary, and this shared sense of wonder forms the basis of their strong friendship. Fuyuki’s heartfelt appeals to this friendship are frequently what stop Keroro’s more serious invasion plans. On multiple occasions, Fuyuki has used his kindness and powers of persuasion to avert global disasters, earning him an informal reputation as a space diplomat.

His key relationships include his family: his mother Aki, his sister Natsumi who often acts as the household's physical defender, and his grandmother Akina. He is also the object of affection for his wealthy classmate Momoka Nishizawa, as well as another student named Chiruyo Tsukigami, though Fuyuki appears to be largely oblivious to their romantic feelings for him. Within the Keroro platoon, his closest bond is with Keroro, but he interacts with all members, often being one of the few who can reason with them. While Fuyuki shows little interest in fighting, he has demonstrated strong willpower when his friends or the Earth are in danger, such as during the Garuru platoon saga where he uses a Kero Ball to defend himself. His development throughout the series is subtle but shows a growing sense of responsibility, as he moves from a passive observer fascinated by aliens to an active protector who uses his intelligence and diplomatic skills to resolve conflicts. His notable abilities lie not in physical combat but in his vast knowledge of paranormal subjects, his unexpected skill as a horror storyteller, and his most powerful asset: the ability to be surprisingly intimidating when pushed to his limits, using his terrifying anger or clever sophistry to defuse situations that violence cannot solve.