Ten no Tori Hana no Yume

Mayuko Eda is a first-year high school student who, when she was young, absorbed a heavenly flower with mysterious powers into her body. Due to the power of the heavenly flower, her body remains immature even as she reaches puberty, causing her to worry about the discord she feels with those around her... One day, she meets a mysterious man at the Koshikake Cedar Shrine in the forest, who demands that she give him a flower in exchange for granting her a wish. Who is this man with large black wings on his back...?!

(Source: Shogakukan, translated)