Ferris Eris, born into the Eris clan bound by duty to protect the Roland monarchy, was forged through childhood exposure to her lineage’s brutal traditions—incestuous practices enforced to maintain bloodline purity. Her brother Lucile halted this cycle by assassinating their parents, dismantling the clan’s legacy and leaving Ferris marked by stoicism and emotional detachment, though fiercely loyal to Lucile despite fearing his merciless nature.

A consummate swordswoman, her unmatched speed and reflexes stem from relentless training rather than supernatural gifts. Her blade houses the "God Devouring" talisman, crafted by Ryner Lute’s father to suppress demonic forces within Ryner—a power that demands her life as collateral, mirroring her readiness for self-sacrifice.

Tasked by King Sion Astal to hunt Rule Fragments alongside Ryner, their partnership shifts from antagonistic jabs to mutual dependence. Ferris conceals affection beneath sharp wit, erupting into fury when Ryner’s death is faked and bristling at rival Kiefer Knolles, whom she pointedly avoids naming. Their bond deepens into a later marriage proposal, signaling her guarded heart’s gradual thaw.

Her obsession with dango fuels comedic escapades, from doubling her snack orders for Ryner to carry to chasing down offenders in a crossover OVA after her dumplings are trampled.

Following Sion’s betrayal, she allies with Ryner in the Anti-Roland Coalition, clinging to faith in Sion’s redemption. Battles against overwhelming foes, including a lethal clash with Miran Froaude narrowly thwarted by Lucile, chart her evolution from aloof warrior to one irrevocably tied to her companions’ fates.

She co-authors a fictionalized chronicle with Ryner, casting themselves as protagonists—a project Sion adapts into lucrative picture books, channeling funds to her sister Iris. Through trials, Ferris transitions from a trauma-scarred guardian to a figure embracing vulnerability, loyalty, and quiet devotion, her principles and bonds ever-steadfast.