Shion Sonozaki, the elder identical twin of Mion Sonozaki, has lived as the “younger” sibling since their childhood identity swap on the day of the family’s oni tattoo ritual. This deception allowed Mion to inherit the Sonozaki heirship, embedding lasting bitterness in Shion toward rigid traditions and her perceived marginalization. Sent to St. Lucia’s boarding school, she fled in 1982 with aid from bodyguard Tatsuyoshi Kasai, hiding in Okinomiya under the guise of a waitress at Angel Mort. To obscure her identity, she periodically assumed Mion’s role. Her life shifted when Satoshi Hōjō rescued her from harassers, sparking an obsessive devotion that fueled her vendetta against his sister Satoko, whom she held responsible for his torment. Though physically identical to Mion, Shion wears a half-ponytail tied with a yellow ribbon. Her wardrobe alternates between a white sleeveless sweater with a black skirt and her St. Lucia uniform—a gray blazer, red tie, and navy skirt. She conceals a stun gun gifted by Kasai. Shion’s charm masks a calculating, volatile nature. Envy over Mion’s status and Satoshi’s disappearance amplified her vulnerability to Hinamizawa Syndrome, triggering paranoia and violent extremes, including orchestrated killings in certain arcs. Yet her later resolve to honor Satoshi’s plea to protect Satoko reshapes her path. She risks her life to challenge Satoko’s abusive uncle and aids legal efforts to secure the girl’s safety. Her bond with Mion weaves love and rivalry. Despite resenting her twin’s position, they share moments of solidarity, even swapping identities. Tensions peak when Mion enacts a family punishment by removing Shion’s fingernails—a cruelty Mion later inflicts on herself in remorse. By Matsuribayashi-hen, Shion opts for restraint over violence, reflecting her growth. This arc underscores her capacity for introspection, mirroring others’ redemptions. Decades later, the Rei sequel briefly notes her marriage to Satoshi. Her past includes aggressive defiance during the dam conflict and an aversion to canned food, rooted in Kasai’s fabricated tales of human meat processing. Each detail threads into the tapestry of her defiance, resilience, and fractured redemption.