Aurica Nestmile, alternately known as Orica Nestmile, emerges as a third-generation Reyvateil born in Skuwat Village on the Wings of Horus. Her hybrid lineage—a human father and Reyvateil mother—condemned her to a fragile existence reliant on the life-sustaining agent Diquility to stave off an early demise. Childhood trauma etched her psyche when, at eleven, her village fell to clashes between Tenba and the Teru Tribe, claiming her parents and embedding survivor’s guilt. This catastrophe spiraled into chronic self-reproach, crippling depression, and isolation, worsened by her stigmatized status as a "D-class" Reyvateil due to stunted song magic prowess. Her fragile psyche clung to a stuffed bear, Don Leon, which later materialized as her Mind Guardian within her Cosmosphere.

Compelled to join the Elemia Church by their Diquility monopoly, she became ensnared in Bishop Falss’s schemes, manipulated into partnering with Lyner Barsett as a pawn to host the rogue AI Mir. Initially guarded and riddled with insecurity, her bond with Lyner sparked incremental growth. Critical moments—rescuing him with Life Warmth Song Magic and thwarting threats like corrupted A.B.R. guardians—marked her tentative steps forward. A turning point arrived during the ELMA-DS conflict, where a viral incursion into her Cosmosphere nearly killed her. Lyner’s intervention to mend the damage ignited her path to healing.

Forced to activate the Hymn Crystal Linker, she unwittingly triggered Mir’s possession, unmasking Falss’s betrayal and Mir’s ruse as the goddess Tyria. Amid the crisis, Aurica’s defiance surged, bolstered by Misha’s Chronicle Key. Subsequent clashes with Falss and Mir honed her resolve, culminating in her contribution to reigniting the tower via the Re=Nation hymn. Returning to Skuwat’s ruins, she confronted her grief, discarding Don Leon and ending letters to her departed parents.

Cosmosphere explorations peeled back layers of trauma and growth, each mental stratum unlocking enhanced song magic and symbolic attire: the childlike "Standard" garb gave way to the transcendent "SERAPH" and "LILIM" regalia, mirroring her ascent from doubt to supremacy as the most resilient third-generation Reyvateil, enduring even Extract-type hymns.

Ancillary tales, like the OVA, depict her grueling efforts to refine song magic while aiding Lyner’s airship repairs, cementing her tenacity to transcend perceived flaws. Her arc, woven with sacrifice and redemption, charts a metamorphosis from fractured vulnerability to unflinching self-acceptance, anchored in the transformative power of trust.