The orphan Katsuko is adopted by her wealthy aunt, but also has to face the bantering of her impulsive cousin Kyou. What's more, they will start attending the same school.

In the new school, Katsuko meets Komori, the haughty president of the singing club (which she joined), the studious and serious Narumi, and the fascinating sempai Saiki. The girl also notices some strange conflicts. Kyou and Komori dislike each other and are constantly competing with one another. Narumi starts to be cold towards Katsuko, convinced that she wants to seduce Saeki, whom she has loved since childhood.

The reason for the hatred between Komori and Kyou is soon revealed: Kyou is in reality the daughter of her father's mistress, who is also Komori's mother. Komori has always been jealous of Kyou since she has a central place in their mother's heart, as she discovered by reading her mother's diary.

It's Katsuko who will finally be able to end the dispute between the two families and make Narumi break into the heart of her beloved Saeki.