Hidetoshi Dekisugi stands as Nobita Nobi's classmate and his academic and athletic opposite. He consistently earns perfect test scores and demonstrates proficiency in various physical activities like baseball, soccer, and track, showcasing agility and endurance. His talents extend to artistic pursuits, including realistic drawing and painting, alongside practical skills such as cooking, household chores, sleight of hand, and magic tricks.

Despite his wide-ranging competencies, Dekisugi maintains a modest demeanor and exhibits consistently polite, gentlemanly behavior. He avoids boasting and displays a rational, scientifically grounded mindset, dismissing superstition. He often encourages others and refrains from speaking negatively about them. This extends to his compassionate treatment of Nobita; he defends Nobita against bullying by Gian and Suneo, emphasizing societal contribution over test scores. Although Nobita frequently expresses jealousy—particularly regarding Shizuka Minamoto—and sometimes attempts sabotage using gadgets, Dekisugi consistently regards Nobita as a friend. He demonstrates this by discreetly assisting Shizuka in baking a birthday cake for Nobita.

Dekisugi shares a close, platonic friendship with Shizuka, frequently collaborating on homework, recreational activities like board games or outdoor painting, and cooking. In one future scenario, he proposed marriage to Shizuka, but she declined, feeling her support would be unnecessary. His future includes becoming an astronaut, marrying, and fathering a son named Hideyo.

His forgiving nature is evident when he chooses to help Gariben, a classmate who resented being second best and attempted to undermine Dekisugi's academic performance through disruptive pranks. After Gariben's actions were exposed, Dekisugi offered study assistance rather than retaliation.

Dekisugi's surname, meaning "exit, leave, go out" (出), "tree, wood" (木), and "cedar" (杉), combined with his given name Hidetoshi, meaning "unusual talent" (英才), reflects his character. His name is also a pun on "dekisugiru" (over-achieving). He is primarily addressed by his surname. In parallel world narratives, his counterpart is unintelligent and scores zero on tests, experiencing bullying from Gian and Suneo. An early manga version assigned him the given name "Taro" before "Hidetoshi" was established.