Yang-yang is a 4-year-old girl facing the tension of her parents separation. In school, she begins to have behavioural problems, and even shows violence towards other children. She refuses to speak to anyone, closing up her inner world.

Until one day, Yang-yang realises her school locker is a secret mailbox that allows her to connect with an Angel Bunny who wishes to be her friend. She tells it her secrets, and so, their friendship blossoms...