After the long-awaited return of the Agent of Spring, Hinagiku Kayo, and New Year's surprise attack on Summer and Autumn, the Four Seasons have formed an unprecedented united front. While they successfully overcame many challenges and hardships, a new challenge has arisen. The Hazakura sisters have become the first dual Agents in history. Is this a good or bad omen? Summer has arrived, and the Agents' story begins once more.