Shion Sonozaki, identical twin to Mion, originated as the elder sibling before childhood role-swapping redirected their fates. Family tradition dictated the exchange during the heir-designation ritual, where Mion received the oni tattoo, leaving Shion to endure St. Lucia’s boarding school. In 1982, aided by family bodyguard Kasai Tatsuyoshi, she fled to Okinomiya, working at Angel Mort restaurant while co-managing the Hinamizawa Fighters little league team. Combining playful mischief with calculated manipulation, Shion balanced rebellion and protectiveness. Her polished St. Lucia demeanor masked simmering resentment toward the school’s rigidity, fueling acts like rumor-spreading to unsettle staff. Envy of Mion’s heir status and unresolved longing for Hōjō Satoshi—whose unexplained disappearance haunted her—left her vulnerable to Hinamizawa Syndrome. The condition intensified her paranoia and violent impulses, driving schemes of vengeance in arcs like Watanagashi-hen and Meakashi-hen, where jealousy warped her actions. Relationships defined her evolution. Blaming Satoko Hōjō for Satoshi’s anguish shifted to a fierce, sisterly protectiveness, honoring his memory by shielding Satoko. This bond pushed her to confront threats like abusive uncle Teppei, initially favoring brutality before adopting legal strategies influenced by Keiichi. Minagoroshi-hen revealed her growth through life-risking defiance to safeguard Satoko, underscoring a capacity for redemption. Physically mirroring Mion with mint-green hair and turquoise eyes, Shion’s yellow ribbon marked her identity. Wardrobe shifts—school uniforms, striped turtlenecks, skirts—tracked her journey from boarding school exile to Hinamizawa reintegration. Though proficient with stun guns and firearms in later arcs, she often avoided lethal force, prioritizing restraint. Decades later in Rei, Shion’s marriage to Satoshi Hōjō resolved her emotional turmoil, contrasting earlier arcs dominated by instability. Matsuribayashi-hen showcased her maturation, employing non-lethal tactics to protect allies, transcending the Syndrome’s grip. The twin dynamic with Mion wove complexity through shared history and diverging environments. External differences masked core similarities, with Rena Ryūgū noting their overlapping identities—Shion’s envy and Mion’s hidden femininity allowing behavioral mimicry while preserving distinct struggles.