Aoi Kirishima, the elder sister of Haruto Kirishima, resides in Tokyo’s Heights Bathhouse dormitory near the Akitsuki family estate. Her striking appearance features long black hair with bangs swept to the left, brown eyes, and a curvaceous frame accentuated by prominent breasts. Contrasting her brother’s maturity, she leans into laziness and irresponsibility, habitually relying on Haruto to manage her chores. Aoi’s carefree lifestyle is marked by heavy smoking and a perpetually cluttered living space.

She influences Haruto’s romantic trajectory by unveiling a childhood photo of him with Yuzuki Eba, openly favoring Yuzuki over Nanami Kanzaki. Later, she departs Tokyo to pursue a teaching license through student teaching in her hometown, signaling a turn toward professional growth. Previously, she attended university in Tokyo and briefly hosted Haruto before his move to independent housing.

Her dependency on Haruto extends to domestic routines, with him often preparing meals during their cohabitation. Though seemingly laid-back, her actions subtly steer pivotal moments, such as rekindling Haruto’s awareness of past bonds and swaying his relationship choices. The surname Kirishima combines “paulownia” and “island,” while her given name, Aoi, signifies “hollyhock” or “althea.”