Isami Ōmiya is Shinobu Ōmiya's older sister, working professionally as a fashion model. She displays considerable talent in clothing design and sewing, crafting elaborate and ornate garments that impress others, including the strict teacher Akari Kuzehashi. While not always practical, her creations showcase her creativity and skill in fashion design.

She is protective and caring towards Shinobu, frequently worrying about her younger sister's absent-mindedness and carelessness. Despite these concerns, she effectively supports and manages Shinobu's tendencies. Her involvement extends beyond guardianship; she actively participates in group activities, collaborating on projects like Halloween costumes for Shinobu and her friends, highlighting her supportive and involved role.

During personal difficulties, such as experiencing a slump, Shinobu and her friends rally to help uplift her spirits, indicating mutual reliance and a deep bond with the main friend group. This reciprocity underscores her integration into their social circle beyond being solely Shinobu's sister.

Her personality balances responsibility with approachability. While maintaining her modeling career and looking out for Shinobu, she also exhibits a playful side, engaging in lighthearted activities with the group. This multifaceted dynamic positions her as a stabilizing yet accessible figure, contributing to both familial and social storylines.