Hijiri Yajima is a main character in the FLCL Alternative story, where she is part of a close-knit group of four high school friends. Within this group, Hijiri is initially presented as the most mature and sophisticated, a perception she actively cultivates among her peers. She has a successful side career as a model, having appeared on magazine covers, and carries herself with an air of confidence and worldliness that sets her apart from her friends.

In terms of appearance, Hijiri is striking, with long, voluminous black hair styled with wispy bangs and sharp blue eyes. She is often seen wearing stylish, fashionable outfits that complement her figure, and her look is typically finished with carefully done manicured nails.

Her personality, however, is more complex than her polished exterior suggests. At the outset, she embodies what her friends, particularly Kana, think of as the pinnacle of adulthood. She dates an older college student named Toshio, a photographer, and seems unbothered by the gossip it generates at school, coolly dismissing the concerns of her classmates. This behavior makes her the object of admiration for Kana, who is desperate to appear more grown-up herself.

As the story focuses on her, it becomes clear that Hijiri’s maturity is largely a performance. Her relationship with Toshio is not a deep, adult connection but a means to an end, a way to bolster her own image as someone sophisticated and desirable. When Toshio abruptly breaks up with her after becoming infatuated with the alien Haruko, Hijiri hides her pain and tries to project an image of cool indifference, insisting that she is fine and that the relationship meant little to her. This facade slowly cracks as she continues to interact with her friends, who can see that her happiness is forced.

Hijiri’s central role in the story is to explore the theme of performative adulthood. Her arc reaches its peak when her friends, led by a well-meaning Kana, confront Toshio about the breakup. In the ensuing chaos, which includes a robot attack born from Kana’s emotional outburst, Hijiri risks her own safety to push Toshio out of the path of a falling light post. Instead of showing gratitude, Toshio immediately panics over his crushed camera. This moment serves as a harsh but clarifying revelation for Hijiri. She stops her friends from attacking him and admits the truth: she is just like him. She had been pretending to be mature and lost sight of what was genuinely important, which was her real friendships.

The key relationships in her life are with her three best friends: Kana, Pets, and Mossan. Kana looks up to Hijiri immensely, and their dynamic drives much of the emotional conflict. Kana’s attempts to "fix" Hijiri’s relationship stem from her own immature ideas about adulthood, but the fallout ultimately teaches both of them a valuable lesson about authenticity. Her friendship with the more laid-back and sarcastic Mossan and the observant Pets provides a grounding contrast to her performed persona.

A notable detail during the climax of her personal story is when she bites off one of her carefully manicured nails, a small but powerful act that symbolizes her shedding of the restrictive, mature image she had constructed for herself. By the resolution of this conflict, Hijiri has seemingly stepped away from modeling and is shown working as a waitress at a karaoke restaurant, embracing a more ordinary and genuine teenage life with her friends. She demonstrates a surprising capacity for empathy by seeing her own flaws reflected in Toshio, which allows her to move past the hurt and mature in a real, rather than superficial, way.