Ryū Nagumo is a first-year high school student in Class C and a member of the Koyo Futsal Club. He possesses medium-length gray hair, green eyes, and stands 160 cm tall, noticeably shorter than his teammates. Despite his small stature, he maintains a positive attitude that bolsters team morale. Though the youngest in his family, which includes parents and an older sister, he acts as an older brother figure to the club's first-year students as the oldest among them. His wealthy family background is indicated by relatives operating a ryokan (traditional Japanese inn) and a gym; these facilities hosted the Koyo Futsal Club's training camp.

An aggressive junior high player who won top scorer honors, his playing style contrasts with his physical size. He longs for an old friend to return to futsal. His birthday is April 21 (Taurus), blood type O. Hobbies include playing video games and enjoying rock music. A special skill is participating in ramen eating contests; ramen is his favorite food, and he has no least favorite food. He likes useful things and strong individuals but dislikes calculation.

His name reflects characteristics: "Ryū" (竜) means "dragon," while "Nagumo" combines "south" (南) and "cloud" (雲). He demonstrates a supportive team role, guiding less experienced members during training. Narrative interactions with teammate Taiga Amakado are noted.