Isaki Magari, born December 23, 2006, lives with Hypoplastic Left Heart Syndrome, a congenital condition leaving only half her heart functional. Her childhood involved frequent hospital stays, and she continues monthly check-ups and surgeries that have left scars beneath her armpit and between her breasts. Fear of dying in her sleep fuels chronic insomnia. In early 2022, she moved to Kurikami City and entered Kuyo High School as a first-year student. She possesses striking black eyes and black hair, usually tied in a traditional chonmage topknot. At school, she dons a uniform: a light blue half-sleeved shirt, blue-and-white striped necktie, black skirt with white stripes, black tights or knee socks, and white Mary Jane shoes. Off campus, she prefers baggy overalls that enhance her childlike aura. Her design features relatively large, wide-set eyes, a small head, a slight shortness compared to classmates, and a cowlick, all adding to her youthful appearance. Outwardly sociable and cheerful, Isaki often smiles and exhibits energetic behaviors like skipping or balancing on objects. However, this carefree demeanor conceals her health struggles; she avoids discussing her heart to evade pity and insists on being treated normally. Her insomnia and uncertain health prognosis foster a seize-the-day mentality, prompting spontaneous acts such as impulsively spending all her New Year's money on a camera. She finds solace in listening to others' heartbeats, a poignant contrast to her own cardiac condition. Key relationships shape her journey. Her elder sister Haya Magari, once distant due to perceived parental favoritism, grows protective. Close friends Motoko Kanikawa, Mina Nono, and Kanami Anamizu offer steadfast support, joining in activities like sleepovers. Her romantic bond with Ganta Nakami sparks when they discover shared insomnia in the school's abandoned astronomy observatory. As they revive the Astronomy Club—where she serves as vice-president—their connection deepens through accidental touches, falling asleep with her ear on his chest, late-night walks, radio app chats, and her initiating their first kiss during a club trip to the Mawaki Ruins, leading to dating. Ganta's consistent lack of pity fuels her affection. Isaki evolves from hiding her conditions to embracing openness about her scars and health fears. She transitions from using the observatory as a refuge to actively engaging in club activities, including astrophotography. Academically, she shifts from aiming for local universities in Ishikawa Prefecture to pursuing opportunities in Osaka after negotiating with her mother. Her romance bolsters confidence in intimacy, allowing her to initiate closeness and navigate boundaries. Ultimately, her narrative centers on living life to the fullest rather than being defined by her health.