Akino Yoake serves as Eim Yoake's older sister, exhibiting a cold demeanor toward everyone except an individual known only as "He" or "Kare." Her unwavering loyalty to Kare dictates her every action and motivation. She explicitly denies any familial bond with Eim, declaring she lost her sibling "two years ago" before the main events—a rejection rooted in Eim's choice to protect Yu Kusaka instead of supporting Akino's cause. This decision forged a permanent rift between them. Akino's allegiance positions her directly against Eim and Yu, compelling her to undermine their interests in service to Kare.

Her Ayakashi, Aterui, manifests as a smaller, crimson-hued counterpart to Eim's Ayakashi, Akuro-ou. This mirrored manifestation accentuates their conflicting loyalties and divergent trajectories.