When fourth-grader Miruku Satou wakes up one morning, she is alarmed to find a grown woman sleeping next to her! But none of her friends and family seem to share her confusion, identifying the woman as her cousin and teacher, Ruu Horie. As the day goes by, Miruku remains unsure whether they have met before—until she notices a pair of wings on Ruu's back.

At the end of the day, Ruu reveals to Miruku that she is actually an angel studying on Earth. Ruu had put a spell on the people around her so that she could easily fit in among humans during her stay, but she's surprised that Miruku is unaffected and can even see her halo and wings. Miruku promises to keep Ruu's angelic nature a secret, and in return Ruu promises to help Miruku whenever she can. Their exchange marks the start of a pure friendship.