Tsubasa Uehara and Arisa Sonoda are identical twin sisters separated by their parents' divorce three years prior. Having only been able to communicate through secret letters, the two arrange to meet up with each other at a park in which they used to play. Nicknamed the "Demon Princess" of her middle school, the tomboyish Tsubasa struggles to get along with the other students in her class. In contrast, the feminine Arisa is the perfect class representative who achieves good grades and has many friends. Learning of her twin sister’s envy, Arisa proposes to Tsubasa that she attend school in her place.

Upon returning from school that day, Tsubasa recounts how amazing her experience was to Arisa, who is horrified to learn that she is still jealous of her life. Telling her sister that she knows nothing about her classmates' secrets nor her own, Arisa attempts suicide in front of Tsubasa's eyes. Determined to uncover the truth behind Arisa's suffering, Tsubasa decides to go undercover to find out.

Now posing as Arisa, Tsubasa witnesses her very first "King Time"—an event that takes place every Friday during fourth period where a wish of Arisa's classmates is randomly granted. Believing the occasion to be a strange joke, Tsubasa does not take it seriously until someone is hurt in the process. Seeing the extent to which the "King" will go to fulfill these requests, Tsubasa must uncover the King's identity and how all of this involves her beloved twin sister.