Chitose Naruse attends Houshou Private High School as a second-year student and class president of Class 2. Her appearance features a slim build, fair skin, dark brown hair styled in two long braids reaching her thighs, light brown eyes, and red-rimmed glasses, often accented with yellow hair clips. She wears the standard school uniform: a mustard yellow blazer, white collared shirt with a red ribbon, blue skirt, black thigh-high socks, and brown loafers. Following an incident where a giant crab consumed her underwear, she temporarily forgoes them. She later modifies her attire, tying her vest and shirt to expose her midriff.

As class representative, Chitose displays strong leadership and commands peer respect. She adheres to a strict moral code, frequently opposing actions she deems unethical, such as Misuzu Jinno's exploitation of classmates. This stance stems partly from witnessing Misuzu engage in a transactional sexual relationship with a teacher. Chitose exhibits selfless dedication to others' safety, prioritizing well-being despite flaws or hostility. She shares a particularly close bond with her best friend, Mutsumi Oribe, displaying protective instincts and emotional reliance. Her interactions with Mutsumi carry romantic undertones, though the relationship's exact nature remains ambiguous.

After surviving a plane crash and washing ashore on Little East Island, Chitose reunites with classmates including Atsushi Kamijo and Misuzu Jinno. She immediately attempts to establish order, analyzing the surroundings and expressing concern for Mutsumi's whereabouts. Her leadership faces challenges when classmates ignore warnings about dangers, leading to fatal encounters with giant insects. She confronts Misuzu over coercive behavior toward Mami Miura, resulting in a physical altercation. Chitose later suffers paralysis and capture by a giant ammophila wasp, which injects anesthetic and attempts to use her as a host for its eggs before Mutsumi and others rescue her.

During refuge at an island clinic, Misuzu restrains Chitose under false pretenses of checking for parasites, leading to sexual assault. When giant crabs attack, Misuzu abandons Chitose while still bound. Freed by Mutsumi, Chitose advocates abandoning Misuzu and Kamijo as punishment, though Mutsumi persuades her otherwise. The group later elects Chitose as their leader over Kamijo. While scouting a path back to the clinic, she witnesses Emiko Miyazono being dragged underground by giant tiger beetle larvae. Retreating to a bamboo forest with Mutsumi, Chitose insists on rescuing endangered classmates. Under Mutsumi's guidance, she crafts a bamboo sword and uses it to fight the larvae, successfully saving Kasumi Momosaki and Misuzu while demanding future cooperation from the latter.

Chitose remains vigilant about group cohesion, backtracking to find Mutsumi when she falls behind and intervening when Mutsumi faces harassment from Ryou Usui. She mediates conflicts between Mutsumi and resistant survivors like Nozomi Aoyama. When giant firefly larvae attack, Chitose defends the group with her bamboo sword, though its effectiveness is limited against the larvae's exoskeletons. She rallies Kazuhiko Kai to help rescue others despite his self-serving attitude, appealing to his past experiences. Later, at a shrine overrun by a giant spider, she pushes Mutsumi and Nozomi out of danger, resulting in Mutsumi's capture. Chitose immediately organizes a rescue effort, but Kamijo physically restrains and binds her to a pole when most classmates refuse to assist. She persists in her commitment to save Mutsumi despite this setback.

Throughout these events, Chitose maintains her core principles of protecting others and upholding moral responsibility, even toward those who betray her. Her relationship with Mutsumi remains a driving motivation, particularly evident in her relentless rescue efforts after Mutsumi's capture. Her leadership is characterized by decisiveness and a willingness to confront threats directly, though she faces persistent opposition within the group.