Hi! School - Love On (2014)

Lee Seul Bi is an angel who was sent to Earth and was tasked to look after Shin Woo Hyun, a young man who lives with his grandmother and carries emotional wounds from being neglected by both of his parents. Despite being coldhearted, Woo Hyun is known at school for his good looks and talent in singing. When his best friend learns about a secret that relates them together and also happens to like Seul Bi, who disguises herself as a fellow student at thier school, these two best friends ended up becoming rivals.