Kouta, the protagonist, and Yuka, are childhood friends who live next to each other. Since their parents are away most of the time, they often go back and forth between their houses and grow up together like siblings.
However, before he knows it, Kouta no longer thinks of Yuka as his sister and sees her as a girl.
Yuka has always been very shy and is naive when it comes to romance. Just by seeing a kissing scene in a drama, her face turns so red and that she has to look away from the screen.
Because of this and afraid of ruining the relationship they have, Kouta doesn't tell Yuka how he actually feels about her.
Don't rush, if we can slowly deepen our relationship...... Kouta continues to spend his days with Yuka while thinking about this.
But, unknown to him, Yuka has changed, and when he finally notices it, she is already――
This is the story of a longing childhood friend who has become a plaything for a classmate.