Coy and self-conscious high school student Karin Karino never paid much attention to boys until she met Kiriya, a popular student from a nearby boys' school. Karin and Kiriya embark on a romantic journey despite Karin's classmate Yuka's best efforts to sabotage their relationship, but Karin soon learns that living happily ever after isn't on the curriculum when she becomes Kiriya's center of attention, as well as embittered Yuka's bull's-eye on her dartboard of hate.

As Kiriya's object of affection, Karin wonders if she can truly deal with the consequences, especially when Yuka's bullying pushes her down a stairway to depression. Later, Kiriya asks Karin to go on a trip over their summer vacation, but their plans take one wrong turn after another. Can Kiriya bring Karin happiness? Or does his love just spell trouble?