Hi! School - Love On (2014)

Synopsis

High school may be tough, but Woo Hyun has a guardian angel looking over him — literally. Disguised as a naive high schooler, Lee Seul Bi descends from the heavens to protect Woo Hyun's life, but discovers she's got a thing or two to learn about life as a teenager, including the pains of falling in love. Can this cherubic guardian protect the apple of her eye and also manage to survive high school?