Nao Toramaru is a high school student and a character in Sakamoto Days. Her background is rooted in a childhood encounter with Taro Sakamoto during his prime as an assassin, which left a profound and lasting impression on her. From that moment, she dedicated herself to becoming worthy of his attention, pushing her physical abilities, learning new skills like music and makeup, and ultimately entering the assassin world. She is introduced during the JCC Transfer Exams Arc as a special recommendation candidate, joining the exam in its third stage.

In terms of personality, Nao presents a stark duality. On the surface, she appears as a cheerful, ordinary schoolgirl with braided black hair and a school uniform, even carrying a handmade Sakamoto keychain on her bag. Beneath this innocent exterior, however, lies an obsessive superfan with intense and unstable tendencies. Her devotion to Sakamoto borders on worship, and she becomes fiercely protective of his image. Any perceived insult toward her idol or even toward her own fandom can trigger a sudden, violent shift in her demeanor. She has no mercy for those who mock her or her fellow fans, and her psychological instability makes her unpredictable in combat. Her motivations are entirely centered on Sakamoto: she seeks his recognition and admiration, and her every action is filtered through her idolization of him. She initially idolized the cold, legendary hitman she saw as a child, but over time she has come to appreciate his better qualities as well.

Nao's role in the story begins as one of several special recommendation candidates in the JCC transfer exam. During the Tail Tag game, she demonstrates her overwhelming combat ability by cutting down trees and ruthlessly disabling opponents to collect tags. Her fixation on Sakamoto influences even her in-game decisions, such as targeting the white team because its color reminds her of Sakamoto's hair. Later, she crosses paths with Shin Asakura, and their interactions highlight the contrast between her idealized memory of Sakamoto as a killer and Shin's respect for the man Sakamoto has become. In a later development, she meets Sakamoto's wife Aoi and his daughter Hana, and rather than resenting them for leading Sakamoto away from his assassin life, she accepts Hana, calling her cute and showing a softer side.

Nao's key relationships center around Sakamoto as her ultimate idol. She also forms a temporary alliance with Shin during the exam, though their differing views on Sakamoto create tension. She is later approached by the antagonist Gaku, who takes an interest in her abilities, but her primary loyalty remains with her admiration for Sakamoto.

Her notable abilities include extraordinary physical strength that contradicts her schoolgirl frame. She fights with a rough, brawler-style technique, relying on raw power and aggression. Her weapon of choice is a custom hybrid of a gun and an axe, allowing her to engage effectively at both close and long range. She is agile and fast, capable of destroying multiple trees in seconds. Her combat style is chaotic and brutal, reflecting her volatile mindset. Beyond her raw power, her psychological instability itself is a weapon, as it makes her actions difficult to predict and her threshold for violence extremely low. Throughout her appearances, Nao shows some development in expanding her understanding of Sakamoto beyond his past as a killer, gradually acknowledging the family and peaceful life he has built.