Makoto Kobayashi died by suicide at fourteen through a sleeping pill overdose before the narrative begins. His despair arose from severe family discord and social isolation, fueled by witnessing his mother's infidelity with her flamenco instructor, his father's weak submission to workplace exploitation through excessive overtime, and his academically successful brother Mitsuru's dismissive attitude. Unrequited feelings for classmate Hiroka Kuwabara, involved in compensated dating with older men, further disillusioned him. An accomplished artist, Makoto channeled his turmoil into painting, though it failed to alleviate his distress.

A disembodied soul, later revealed as Makoto's own, is forcibly placed into his revived body by the entity Purapura. This reincarnation carries specific conditions: the soul must uncover both the "great sin" from its past existence and the reasons behind Makoto's suicide within six months. Upon revival, the soul experiences profound disorientation and amnesia regarding its identity and past life. Initially apathetic and resistant to this second chance, it struggles to navigate Makoto's relationships and responsibilities. Crucially, the soul discovers it cannot replicate Makoto's artistic abilities, symbolizing its emotional disconnect. Purapura serves as an observer, offering minimal guidance while enforcing the strict time limit.

Within the family, the soul initially mirrors Makoto's resentment. It reacts with visceral hostility upon learning of the mother's past affair, despite her attentive caregiving efforts to atone. The soul perceives the father as ineffectual due to his passive endurance of workplace bullying, unaware of his hidden integrity in challenging corporate corruption years before. Tensions escalate with Mitsuru, who prioritizes academic achievement and views Makoto's resurrection as disruptive. This friction manifests in strained mealtime interactions where the soul's contempt clashes with the parents' attempts at reconciliation.

School life presents further complexities. The soul develops conflicted relationships with three classmates: Hiroka continues her transactional relationships, dismissing the soul's attempts to "rescue" her by asserting autonomy over her body and choices. She admits to fluctuating between hedonism and despair, yet the soul gradually learns to accept her decisions without moral judgment. Shoko Sano, an observant and socially awkward classmate, recognizes the soul's altered behavior and voice, leading to suspicion and confrontations that force the soul to acknowledge her perceptiveness. Saotome, an academically disinterested but kind-hearted peer, becomes Makoto's first genuine friend. Their shared aimlessness evolves into mutual support, including collaborative studying for entrance exams, providing the soul's first experience of uncomplicated camaraderie. This friendship proves pivotal in reshaping the soul's outlook.

Character development culminates in two intertwined realizations. First, the soul uncovers its identity as Makoto Kobayashi, with his "great sin" being the act of suicide itself. This revelation occurs as the six-month deadline expires, contextualizing his prior detachment and anger as manifestations of unresolved guilt and self-loathing. Second, Makoto achieves a nuanced understanding of human imperfection through key interactions: recognizing his mother's remorse and efforts toward unity, acknowledging his father's quiet resilience despite workplace injustices, appreciating Mitsuru's suppressed care (evidenced by his willingness to delay college for Makoto's education), and accepting Hiroka's autonomy without condemnation. This maturation is symbolized by his renewed appreciation for art as an expression of life's multifaceted nature, not an escape. The narrative concludes with Makoto choosing to embrace existence with its inherent struggles and complexities.