Sakuta Azusagawa, a high school student at Minegahara High, begins isolated due to false rumors about a "Hospitalization Incident" where he supposedly hospitalized others violently. This reputation emerged after he received three mysterious claw-like scars on his chest during his sister Kaede Azusagawa's struggle with Adolescence Syndrome—a phenomenon translating emotional turmoil into physical or supernatural effects. Kaede developed dissociative identity disorder after severe online bullying, resulting in self-harm injuries and amnesia. While hospitalized for his own chest wounds, Sakuta met Shoko Makinohara on Shichirigahama Beach. Her advice to live kindly profoundly shaped him. In solidarity with Kaede, he discarded his phone into the ocean, an act that fueled the damaging rumors. He displays stoicism, deadpan humor, and a blunt, often lewd speaking style, masking profound selflessness and compassion. Despite societal rejection, he actively helps others afflicted by Adolescence Syndrome, believing enduring widespread hatred is worthwhile if even one person needs him. His resilience stems from Kaede's ordeal and Shoko's mentorship. His life shifts dramatically upon encountering Mai Sakurajima, a famous actress rendered invisible to others by her own Adolescence Syndrome. As the sole person who can see her, Sakuta investigates her condition, sparking a romantic relationship. He restores her visibility by publicly declaring his love, defying school norms. Their bond strengthens while navigating challenges like Mai's demanding career and their fierce mutual protectiveness. Mai later sacrifices herself to save him from a traffic accident, a pivotal event. Sakuta's relationship with Kaede remains central. After their mother's breakdown, he becomes her primary caregiver, moving into a separate apartment to aid her recovery. He encourages her gradual reintegration into society, documenting progress in a diary. When Kaede regains her original memories but loses two years of experiences—erasing the persona Sakuta knew—he grieves yet accepts her, committing to rebuild their connection. The appearance of Shoko Makinohara—both as a middle schooler with a fatal heart condition and an adult from an alternate future—triggers significant development. The adult Shoko reveals she received Sakuta's heart after his altruistic death in her timeline, having time-traveled to save him. Sakuta initially plans to sacrifice himself for her, but Mai intervenes and dies instead. Devastated, Sakuta uses time travel to prevent both deaths, creating a new timeline where Shoko survives without a transplant but loses her memories of him and Mai. Ultimately, Sakuta and Mai encounter a healthy Shoko bearing fragmented memories of their shared pasts. In later years, Sakuta matures into a university student and part-time cram school lecturer, maintaining his commitment to aiding those with Adolescence Syndrome. His core trait—selflessness rooted in Shoko's philosophy of kindness—persists, driving his actions through ongoing emotional and supernatural trials.