Asagi is a central figure in the narrative of Shibuya, a fifteen-year-old girl who serves as the leader of one of the three primary gangs, the Love Generations. Her role in the story is complex, beginning as an ally to the protagonist Tsuyoshi before a significant act of betrayal that defines much of her character arc. Her journey is heavily influenced by the oppressive rules of the virtual Shibuya, particularly the threat of being "broken" and "reset" by the enigmatic enforcer, Piece, which results in the complete loss of one's identity and memories.

Asagi’s background is rooted in the daily struggle for survival and influence within the closed-off city. She is first encountered when Tsuyoshi helps her fight off members of the rival Bunkamu gang, immediately establishing her as a figure caught in the constant territorial conflicts. She is practical and well-informed about the workings of this world, as she is the one who later briefs Tsuyoshi on the three gangs' names, their leaders, and their territories. Despite her position, Asagi is not immune to the dangers of Shibuya; she is marked by Piece, which labels her a "yojire," someone destined to be killed, a status that carries a heavy social stigma.

Driven by a desire to return to her gang and escape the shame of being marked, Asagi's primary motivation becomes self-preservation and the restoration of her place within the social order. This desperation leads her to make a deal with Ryuugo, the leader of the Palhands gang, who promises to help her regain her status. In exchange, she agrees to betray Tsuyoshi and the mysterious girl Ema, who has the power to temporarily defeat Piece. Asagi lures them into a trap, leading to an ambush by all three gangs in an abandoned parking lot. This act of betrayal highlights her pragmatic and flawed nature, choosing survival and belonging over loyalty.

However, Asagi is not defined solely by this treachery. In a pivotal moment during the ambush, she has a change of heart and helps Tsuyoshi and Ema escape to the boundary of Shibuya. This redemption is short-lived. Later, after being convinced to return to her role as the Love Generations' boss, she discovers the painful truth that her memories of her family are fabrications, not real. In her attempt to flee the city, she is killed by a train. Her death is a significant emotional blow to Tsuyoshi, who mourns her loss, only to learn the cruel nature of Shibuya: the dead are eventually reset.

As a result, Asagi returns as a new person named Miu, having lost all memories of her previous identity. She joins a different gang, the Palhands, and has no recollection of her past as Asagi or her relationships with Tsuyoshi or Ema. This transformation into Miu is the final stage of her development, serving as a tragic illustration of the series' central theme of lost identity and the struggle against a system that constantly erases the self. Her key relationships are consequently severed, leaving Tsuyoshi as one of the only people who remembers her original existence. Asagi does not possess any notable supernatural abilities like Ema; her significance comes from her very human struggles with loyalty, fear, and the desperate desire for a place to belong in a world that is designed to deny her one.