Masato Wakamatsu makes a bad impression on his crush, Miyuki Kashima, while working at a beach one summer. Embarrassed, he flirts with another girl, who turns out to be his stepsister, also named Miyuki, home after six years abroad. When school starts, Masato begins dating Miyuki Kashima, yet he finds himself falling for his stepsister, who may not know they aren’t related by blood.