Nagi Rokuya, a member of IDOLiSH7, possesses striking blond hair and blue eyes, embodying his self-proclaimed "sexy and elegant" aesthetic. He stands as the group's second tallest member. Born in the fictional northern European nation of Northmare (or Northmeir), Nagi is of mixed heritage, with a Japanese mother and a Northmarean father. His full name, Nagi Valhart von Northmare, reveals his identity as the nation's second prince, elder brother to Seto Ranvalt von Northmeir. This royal lineage shaped his upbringing, marked by isolation due to his status, mandatory monthly public meetings, and rigorous training in hand-to-hand combat, firearms, and assassination prevention.

Childhood loneliness defined Nagi's early years; other children avoided him because of his royalty. He wore formal suits from a young age and lacked any friends. This solitude ended when he met Haruki Sakura, the composer for the legendary idol Zero, who journeyed to Northmare seeking Zero. Falling ill, Haruki entrusted Nagi with musical scores meant for Zero, urging him to find someone to sing them. This mission drove Nagi to Japan, intending to anonymously deliver the songs to Takanashi Productions. While scouting near the agency, he encountered Otoharu Takanashi and was recruited into IDOLiSH7.

Nagi displays flamboyant confidence, frequently flirting and declaring himself a "prince," though he has never dated. He harbors a deep passion for Japanese pop culture, especially anime. His room overflows with figurines and memorabilia from his favorite series, *Mahou Shoujo Magical★Kokona*; this obsession once nearly caused him to skip a performance for an anime event. He speaks accented, broken Japanese and is multilingual, fluent in eight tongues: Northmarean, English, German, Norwegian, French, Italian, Japanese, and Chinese.

Beneath his playful exterior lies sharp intellect and diplomatic skill. His royal background equipped him to manage high-pressure public situations, such as leading press conferences for Takanashi Productions as a PR manager. He reassured Otoharu of his capability by citing his experience hosting Northmare's monthly populace meetings. Nagi fiercely guards his identity; confronted by individuals attempting to expose him during a bomb threat, he silenced them violently, declaring they had "no right to say his name."

He treasures IDOLiSH7 as his first true friends, demonstrating loyalty through habits like hugging every member before bedtime—pursuing them if they retreat to their rooms. He deliberately provokes reactions, such as touching Iori Izumi's butt to elicit a scream. Nagi mediates group conflicts and supports members emotionally, notably through efforts to include Tamaki Yotsuba. Playful nicknames characterize his relationships; he calls Yamato Nikaido "Yamato" and Sogo Osaka "Sogo," while they reciprocate with "Nagi" or "Nagi-kun."

His development shows increased group integration and acceptance of his dual identity. Initially secretive about his royal ties, he gradually acknowledges them, particularly during crises demanding his combat skills. His bond with Sogo Osaka is highlighted by shared refined tastes from their privileged backgrounds. Nagi also confronts his strained relationship with his older brother, though specifics remain undisclosed.

Nagi exhibits several quirks and fears, including an aversion to ghost stories. After jokingly requesting "chilling stories" from Sogo, he endured nightly readings of *100 Ghost Stories*, believing stopping prematurely invited misfortune. He struggles intensely with Japan's summer heat, relying on Mitsuki Izumi for acclimatization walks and Yamato for cooling treats like shaved ice.