Mio Hirahara, Hiori’s reserved older sister, cloaks her disciplined exterior with unwavering devotion to her sibling’s safety. After their father’s death and mother’s disappearance under the guise of purchasing lightbulbs, Mio shouldered dual roles as breadwinner at Platanus and household guardian, burying her anguish to preserve Hiori’s optimism. This self-sacrifice hardened into emotional detachment, masking her turmoil beneath pragmatic responsibilities.

Her attempt to enrich Hiori’s life through Tsukinomiya Girls’ High School backfired catastrophically when Hiori perceived enrollment as rejection. The resulting emotional rupture destabilized Hiori’s Fragment, fueling Mio’s spiral into despair during the Netzach crisis—a failure that shattered reality. Post-timeline reset, Shino Mizusaki exploited Mio’s unresolved guilt, grafting restored memories to recruit her into the Rouge Reflectors. Convinced emotional erasure would spare Hiori pain, Mio wielded chain weapons in a corrupted Reflector form marked by crimson streaks and a tattered apron-like sigil, embodying her fractured resolve.

As Shino’s enforcer, Mio confronted Blue Reflectors Hiori and Ruka Hanari, enforcing emotionless ideals until Hiori’s heartfelt plea during the Saint Inés Church assault cracked her armored resolve. Shino’s interference intensified Mio’s corruption, but Niina Yamada’s timeline revelations exposed Shino’s manipulations. In the ensuing clash, Hiori’s persistent empathy severed Mio from external control, reigniting her agency.

Later, within *Blue Reflection: Second Light*’s mysterious academy, amnesiac Mio retained only ghostly impressions of Hiori. Though Hiori initially withdrew, collaborative investigations into the school’s secrets rekindled their bond. Despite fragmented memories, Mio’s innate protectiveness and tranquil demeanor persisted, quietly safeguarding her sister amidst uncertainty.

Mio’s journey mirrors the duality of chains—tools of control and bonds of love. Her evolving Reflector aesthetics and combat tactics chart a path from suffocating guardianship to liberated partnership, anchored by Hiori’s influence. Each strategic chain maneuver and corrupted mark reflects her internal war between self-destructive guilt and the redeeming power of familial trust.