Upon enrolling at the prestigious Lillian Girls' Academy in Tokyo, Yumi Fukuzawa is taken aback when the charming and graceful Sachiko Ogasawara, a popular figure at the school, selects her to be her 'sister' or soeur, offering guidance throughout her academic journey. This unexpected proposal leaves Yumi in a whirlwind of emotions as the campus gossips about their newfound connection. Despite her admiration for Sachiko, Yumi grapples with the spotlight and scrutiny that would come with accepting this significant role in the school community.