Yuko Yoshikawa teaches music at Siren Academy while balancing her role as protective older sister to Atsuko Yoshikawa. Her piercing blue eyes and cascading curls of dark bluish-black hair, reaching her waist, mirror her enigmatic presence. Skilled in both organ and violin, she channels these talents to disrupt the psychological turmoil inflicted by supernatural forces on students—though her interventions offer only fleeting relief. Her haunting performances occasionally capture the attention of Professor Goda, whose clandestine ties to the tentacled entity beneath the academy linger at the edges of their interactions.

Bound by familial duty to shield Atsuko, Yuko navigates a fractured relationship strained by her sister’s secret romance with Sayaka Matsumoto. Tensions simmer as she wrestles with loyalty, duty, and the shadows of unspoken truths between them.