Sō Hishigata, a 17-year-old resident of Hitogashima, serves as the eldest son of the family operating the island's sole hospital, the Hishigata Clinic. Driven by a strong sense of justice, he studies to become a doctor. This path is fueled by deep regret over witnessing Ushio Kofune's drowning accident without being able to intervene, compounded by his father Seido Hishigata, the clinic director, withholding critical autopsy information about Ushio's strangulation marks. Shinpei Ajiro's childhood best friend, Sō harbors unrequited feelings for Mio Kofune and has confessed to her twice, facing rejection both times. He possesses messy brown hair and brown eyes. In early timeline loops, Sō prioritizes protecting others; during the third loop, he shields Mio from an axe attack by his own shadow, sacrificing his life. In subsequent loops, he becomes integral to investigating the island's shadow phenomenon. He assists Shinpei and Ushio's shadow in exploring the abandoned Hishigata Clinic, discovering tunnels leading to Hiruko's lair. There, Sō witnesses his father collaborating with the shadows and learns of his family's 300-year legacy of serving them. Sō's background as a former baseball player aids him in combat against shadows. He utilizes baseball bats and nail guns—the latter modified by Ushio's shadow—to fend off attacks. He survives a kick from Ushio's shadow and withstands nail gun rounds while wearing protective gear. A critical development occurs in the fourth loop when Sō intercepts a bullet meant for his sister Tokiko, demonstrating his willingness to sacrifice himself for family despite their conflicts. Later, he confronts Seido after saving him from choking; Seido discloses plans for the Hishigata family to become shadows under Hiruko. Sō rejects this legacy, physically attacking Seido upon learning of his mother Chitose's death years prior and the clinic's role in feeding patients to shadows, including Shinpei's parents. In the final loops, Sō participates in strategic battles against the shadows, including protecting Ginjiro Nezu alongside Mio and Tokiko. He reconciles with Tokiko after her betrayal is revealed and joins the united effort to defeat Shide and Haine. Following the conflict, Sō continues pursuing medicine, symbolizing his commitment to preserving life in contrast to his family's exploitation. His character arc transitions from guilt-driven vulnerability to proactive resilience through rejecting familial corruption and upholding his ethical ideals.