Ep. 4: Hiyori Possesses Mitsuki to Impress Yūya Before Returning to Normal

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Hiyori possesses Mitsuki to act as the ideal sister for Yūya, surprising him with breakfast and gentle behavior that makes him smile. Mitsuki observes this, initially dismissing it as flattery, but feels touched when Yūya encourages Hiyori to be herself. During a rock-skipping outing, Hiyori claims to be the friend who called Yūya "big brother," causing confusion when she cannot return to her body. That night, Hiyori uses the thunder as an excuse to sleep in Yūya's room, but his advice to be authentic moves Mitsuki, allowing her to reclaim her body. Embarrassed by the events, Mitsuki kicks Yūya out and resolves to act naturally as he suggested.