During summer vacation, Seika goes to the Kingdom of Astilia in place of his father to investigate a dragon. After researching it and forming a hypothesis, he decides to head to the mountain where the dragon lives and see it for himself. In his absence, Yifa is aggressively pursued by Cecilio, the prince of Astilia. While Seika is out trying to resolve the kingdom's problems, Cecilio begins taking steps to free her from Seika. To make matters even more complicated, the mercenaries hired by Cecilio seem to have their own goals. Will Seika be able to solve the dragon issue while satisfying everyone? And what will Yifa choose, now that she's been left to decide her own future?