Hideyoshi Soya is a character who initially appears as an opponent but ultimately becomes a valuable member of the main group. At thirteen years old, he works as a caretaker at the Sun House, an orphanage for children. His distinctive appearance includes orange and brown hair and a face often compared to that of a monkey, and he has a noticeable habit of moving his ears whenever he is devising a clever scheme or trick.

As a person, Hideyoshi is a study in contrasts. On one hand, he is prone to cowardice and will often try to escape from dangerous situations, favoring sneak attacks and deception over direct confrontation. He is a natural trickster who uses various novelty gags and lies as tools in a fight, with one of his signature moves being a so-called soy sauce bomber. The children at the Sun House have given him the nickname "Tricky" or "Slick" for this very reason. However, beneath this unreliable exterior lies a deeply caring individual. His primary motivation is the protection of the children at the orphanage, and he is known to be genuinely skilled at taking care of them. Despite his dishonesty in battle, he is described as a terrible liar with a kind heart when it comes to the people he truly cares about.

Hideyoshi’s journey into the battle of supernatural powers is unique. He was granted his ability by a Celestial King Candidate named Nero, a kind being who simply wanted to stay on Earth to help the children at the Sun House. Hideyoshi offered to become a power user so that Nero could have a reason to remain in the human world. However, when Nero broke the rules to save Hideyoshi during a fight, he was sent to Hell as punishment. After this loss, Hideyoshi was assigned a new, corrupt candidate named Zack, whom he despises. Zack attempts to force Hideyoshi to join a team of malicious power users by threatening to destroy the Sun House.

It is at this point that Hideyoshi crosses paths with Kousuke Ueki and Ai Mori, who are searching for a final teammate for the tournament’s second round. Hideyoshi agrees to join their team not out of ambition, but because he learns that helping Ueki might provide a way to save Nero from Hell. His relationships with his new teammates are built on this practical alliance, but he becomes known as a member of Team Ueki. While Ai Mori affectionately teases him as the "useless member" of the group, his trickery proves to be a significant asset in battle. For instance, he once used his power to attach voice portraits to a teammate's towels to launch a coordinated sonic attack on an enemy team.

Hideyoshi’s character develops as he overcomes his self-doubt and cowardice for the sake of his friends. Although he often views himself as weak, he finds the courage to fight when those he cares about are in danger. In a critical moment, he gives Ueki a final surge of power, leading another teammate to call him the "secret savior". His notable ability allows him to turn voices into portraits. The condition for using this power is that he must bend his fingers or toes. Once activated, he can create a portrait that can replicate the captured voice. He most often uses this offensively, turning his opponents’ own voices against them or creating distracting noises, combining his sly personality with his unique power to outwit stronger foes.