June the Little Queen Series by Yeon-Joo Kim

Class rivals June and Lucia vie for the honor of being named the Queen of Light, entrusted with protecting the people from the King of Darkness. June is an attractive girl whose feisty, hot temper and general laziness may prevent her from receiving the crown...Lucia has a more regal quality and a strong desire to match, but she is always overshadowed by June. Will petty jealousies, love triangles, and one cute boy interfere with the Queen's royal duty?!

Demons invade the Academy, intent on capturing Sejuru... But what is it about the mysterious young student? Sejuru desperately tries to fight them off, but is soon overcome despite a valiant effort. Sensing her friend is in mortal danger, June breaks free from the confines of the Academy Library and comes to Sejuru's defense. But will it be enough?

The Queen of Light's palace festivities have commenced! As Sejuru and the queen candidates impatiently wait for the crowning ceremony, Lucia and Yuri are getting leery of June and her possibility of being crowned "Your Royal Highness." But while everyone is caught up in the festival, a demon seems to be lurking in the shadows with an eye on one of the contenders...

June reminisces how happy she once was with Sejuru. Meanwhile, Sejuru is feeling different things that he cannot understand. The woman of the underworld keeps saying that his moment of sleep is over and he will be the prince of darkness, which is something he does not want to face.

When Mayanne finally recognizes Sejuru, he is sent to the dungeon, where he must either remain forever or be killed. Upon hearing voices that tell him he is the "precious one," Sejuru manages to escape. But a deadly case of mistaken identity puts a halt to his plans, and he is forced to confront the queen alone...

June tries to convince Sejuru to stay, but instead he goes to the Demon Castle where he hears the story of the Demon King. He learns that the Queen of Light contained the Demon King's powers by cutting him up and sealing his energy. And as if that wasn't enough, it's revealed that June's grandmother ran away with June because of Yuri's prophecy that if June becomes queen, she will have the shortest term in history!