Nagahiro Sakiguchi holds the position of vice president in the Pretty Boy Detective Club, an unofficial group at Yubiwa Academy Middle School. A third-year student, he secured the student council presidency for three consecutive terms immediately after enrollment, thanks to a supremely eloquent orientation speech that mesmerized the entire student body. This feat earned him the club moniker "Nagahiro the Orator," highlighting his exceptional vocal talent.

He possesses long silver hair, usually tied in a ponytail with a black bow, gray eyes, and a tall build. His modified school uniform features a dark green lapel-less blazer with three silver buttons, a white shirt sporting a black neck-covering collar, black and white striped pants, and white high-heeled shoes. He always wears black gloves. Manga depictions sometimes show a more conventional uniform, occasionally including a purple tie and silver knee-high boots.

Born into the affluent Sakiguchi family, his parents arranged his marriage to Kodaki Kawaike, a first-grade elementary school heiress from the declining Kawaike family, to provide financial aid. Club members frequently tease him as a lolicon because of this, prompting his consistent clarification that the marriage was not his choice. Nevertheless, his privileged upbringing instills a sense of duty, compelling him to honor familial obligations.

Nagahiro maintains a composed, soft-spoken, and well-mannered demeanor, acting as the club's most mature member. This maturity helps balance the eccentricities of others, though he retains the requisite childish spirit for club participation. He demonstrates significant intellectual cunning, successfully outsmarting professional criminals like Rei and matching wits with rivals such as Rai Fudatsuki. His sense of duty motivates actions like accepting the arranged marriage and offering friendship to the lonely Mayumi Dojima.

His primary ability centers on his captivating voice, admired even by professional voice actors. Beyond its natural beauty, he exhibits precise vocal manipulation, skillfully mimicking others' voices—a talent strategically valuable during investigations. He functions as the club's liaison officer, leveraging his oratory skills for coordination and puzzle-solving.

Within the club, he shares a notable rivalry with Michiru Fukuroi due to contrasting social standings, though they cooperate during activities. He holds mutual respect for leader Manabu Sotoin and accepts the nickname "Senpai-kun" from Mayumi Dojima after she initially addressed him formally as "Sakiguchi-senpai".

His development shows increased integration into the club, transitioning from occasional collaboration to sustained involvement. He appears in expanded universe content like *Mazemonogatari*, a crossover with the *Monogatari* series, where he visits the North White Snake Shrine under Manabu's direction for celestial observation.