Nami Aoi is the younger twin sister of Sora Aoi, sharing a nearly identical physical appearance distinguished only by slightly darker hair and red eyes in animated adaptations. As children, she frequently impersonated Sora, but their personalities diverged sharply with age. Unlike Sora's quiet compliance, Nami developed a blunt, stubborn, and harsh demeanor, prone to jealousy and possessiveness—traits manifesting early in acts like destroying Sora's toys. She habitually forced Sora into cross-dressing and cosplay for her amusement, ignoring his discomfort and protests, even tearing up his club resignation letter.

Secretly, Nami harbored a profound romantic obsession with her classmate and close friend Kana Sumiya. Paradoxically, she manipulated events to push Kana and Sora together. Witnessing their sexual encounter triggered a psychological breakdown. Consumed by rage and despair, fueled by the delusion that lacking male anatomy prevented Kana's love, she assaulted Sora with scissors, nearly castrating him and slitting his throat. She then raped him while fantasizing about Kana, silencing him with threats of emasculation and death.

After this trauma, Nami initiated an ongoing sexual relationship with Sora, driven by a complex tangle of guilt, latent attraction, and a compulsion to experience Kana's scent through him—especially after his encounters with Kana. Though she verbally expressed disgust, she grew increasingly dependent on these interactions, blurring obsession and potential emotional connection. This fostered an unexpected closeness noted by their older sister Aki, even as it worsened Nami's instability. Her internal conflict intensified, questioning whether her fixation on Kana was genuine love or mere obsession, while reflecting on the growing emotional distance from Sora.

The situation evolved when Kana discovered Nami and Sora together, leading to a consensual encounter among the three. During this, Nami's long-hidden feelings for Kana were finally revealed and acknowledged.