Itsuki is a member of the astronomy club, which secretly operates as a group of magical girls tasked with collecting engine fragments scattered across Earth to help an alien from the Pleiades return home. Her role in the group is central to the team's dynamic, where she is known for her kind and considerate nature. Among her fellow magical girls, her designated thematic color is indigo.

The foundation of Itsuki's personality is rooted in a specific incident from her childhood. She was originally a tomboy with an adventurous and bold spirit, but a serious accident changed her behavior. Defying her brother's warning, she climbed a tree, fell, and received a lasting scar. The accident led to her brother being unfairly blamed for not stopping her. Overwhelmed by guilt, Itsuki made a conscious decision to suppress her own desires and wilder impulses to avoid causing trouble or pain for others. This event transformed her into a person who is consistently gentle and deeply concerned with not inconveniencing anyone.

Despite her typically reserved and selfless demeanor, Itsuki is capable of displaying a fierce and combative spirit. This side of her is particularly evident when she is opposing an antagonist, showing that her core strength remains intact beneath her calm surface. Her personal development arc centers on her struggle to voice her own needs and reconcile her natural selflessness with the healthy expression of her individuality. Through the support of her patient friendships within the club, she begins to learn that being occasionally assertive is not selfish and can actually strengthen genuine bonds. This internal conflict is highlighted during a school festival play where she is initially cast as a princess. Eventually and more comfortably, she switches to play the prince, a role that allows her to reconnect with her true, bolder self.

Her key relationships are primarily with her fellow club members, who provide the supportive environment necessary for her growth. She also has an older brother; their shared history is the catalyst for her initial personality shift, and her deep care for him is a significant motivation for her actions. Within the group's mission, Itsuki is frequently the emotional anchor and a voice of stability, providing a calming presence to balance the other members' personalities. Her notable abilities are tied to her magical girl transformation. Like the others, she flies on a magical broom to search for engine fragments and utilizes unique magical powers, often demonstrating a strong fighting spirit when the situation demands it.