Sweet Revenge follows the life of Ho Goo-hee, a timid and ordinary high school student who is constantly bullied and taken advantage of by her peers. Her life takes a dramatic turn when she discovers a mysterious mobile application called 'Revenge Note.' When she types the name of someone who has wronged her into the app, the person receives a taste of their own medicine, leading to a series of comedic and satisfying consequences. As Goo-hee navigates the complexities of high school, she finds herself caught in a love triangle between her childhood friend and a popular, mysterious classmate. With the help of the app, she begins to stand up for herself and those she cares about, ultimately learning valuable lessons about friendship, justice, and self-worth while uncovering the identity of the person behind the app.