High school may be tough, but Woo-hyun (Nam Woo-hyun) has a guardian angel looking over him — literally. Disguised as a naive high schooler, Lee Seul Bi (Kim Sae-ron) 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?