Ronie Arabel hails from a sixth-class noble family within the Underworld's Human Empire. She enrolls at Centoria's Sword Mastery Academy, determined to elevate her family's status through her swordsmanship. Though she ranks among the year's top twelve trainees, her low noble standing leaves her overlooked by higher-ranking elite swordsmen during valet selection, a fate shared by her close friend Tiese Schtrinen. Consequently, both are assigned as valets to the commoner duo Kirito and Eugeo, the only elite swordsmen remaining without valets.

Serving as Kirito's valet, Ronie trains under him, developing profound respect and admiration unaffected by their differing social ranks. Her personality is reserved and shy, contrasting with Tiese's outgoing nature, but the two share an exceptionally strong bond and are rarely apart.

The Underworld War entrusts Ronie and Tiese with caring for Kirito after Eugeo's death leaves him severely traumatized. They remain steadfastly by his side in Rulid Village, grappling with Eugeo's loss. Later, when Alice departs for the war front, she leaves Kirito in Ronie and Tiese's continued care.

Ronie witnesses the Dark Territory's invasion and participates in the Human Empire's defense. Her experiences, shaped profoundly by the war and her relationships with Kirito, Eugeo, and Tiese, reflect the conflict's impact on the Underworld's younger generation.