Haruka Tosabori is Yukiya Araki's close childhood friend and a supportive high school classmate, deeply involved in his musical activities. Her own life revolves passionately around music; she founded and actively writes lyrics and composes for her band, "More Violent," constantly seeking inspiration and building connections within the music scene.

Typically cheerful and optimistic, Haruka maintains a positive outlook, though challenging situations can sometimes reveal underlying distress or frustration. She pursues her musical ambitions with strong determination and independence.

Her personal life is marked by significant family circumstances. Her mother's hospitalization contributes to feelings of loneliness, while her father, an influential figure in the music industry, remains largely absent. Haruka channels the emotional weight of this pain and sorrow into her songwriting and musical expression.

Her connection to the core conflict begins unknowingly when she assists Yukiya with a music video. Unaware he is an irregular Hand Shaker, she accompanies him into the Ziggurat dimension. There, she experiences a strange vision. Though she forgets the incident upon returning, this marks her first encounter with the story's supernatural elements.

Throughout the narrative, Haruka remains a constant, supportive presence for Yukiya, discussing matters with him and showing concern for his well-being. Her interactions sometimes reveal fluster, hinting at deeper feelings beyond friendship. While primarily supportive, her established background as a musician navigating personal adversity provides context for her motivations and emotional depth.