Although high school is difficult, Woo Hyun (Nam Woo Hyun) has a guardian angel watching over him. Lee Seul Bi (Kim Sae Ron) descends from the heavens disguised as a naive high schooler to safeguard Woo Hyun's life, but she soon realizes she has a lot to learn about adolescence, including the hardships of falling in love. Will this cherubic protector be able to protect the apple of her eye while still surviving high school?