Ryōko Shirakawa is the middle sister of the three Shirakawa siblings. She possesses brown hair, striking red eyes, and a recorded physique of 165 cm tall, weighing 50 kg with measurements of 90-56-82 cm.

Working as a school nurse, her professional environment differs from her older sister Kyouko's nursing role. Ryōko's personality is friendly and open-hearted, frequently offering emotional support within her family. She holds deep affection for her stepbrother, Yuu Shirakawa, a fondness originating during his childhood visits that persists strongly after he moves in following their parents' remarriage.

Crucially involved in the storyline concerning the cursed Vial of Inanna, Ryōko actively participates by providing the bodily fluids necessary to break Yuu's curse. Her interactions with Yuu feature prominently throughout the narrative, encompassing intimate moments in private settings like her bedroom and group encounters involving all three sisters.

Her character background remains unchanged across related media, with her role consistently focused on familial dynamics and resolving the central curse plot.