Haruka Hani is a second-year junior high school student who goes to a school called Hinomori Gakuen. A member of the school drama club, she has been working on the script for a play the club plans to put on at the upcoming school festival. She’s been having trouble finishing it, and her childhood friend Tamaki Teijou has been urging her to hurry up. All in all, she seems to be enjoying her life. From time to time, monsters called Zaiju (Beasts of Sin) appear and attack Hinomori, the town where Haruka lives. But the Heart Princesses are there to fight the monsters. Haruka looks up to these princesses who protect the people of Hinomori from the Zaiju, wishing that she too could be a princess someday. Then one day, when she is working on the script at home, a mysterious cat named Jin comes to her and says, “You seem to have the right qualities to be a princess. What do you think? Would you become a princess?”