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.
Karin's overprotective father foils her plan to spend Christmas Eve with Kiriya, but the two manage to meet anyway. Kiriya gives Karin a pair of diamond earrings, but Karin's friend and confidante Nanri warns her about the earrings' symbolic meaning as a gift. Meanwhile, Kiriya invites Karin to a trip to the mountains to observe the photo shoot of Shinji Takagi, a good friend of his late brother Yuji, but a rainstorm finds them alone together at a sleazy hotel room for lovers. Will Karin finally conquer her fear of intimacy and "go all the way" with Kiriya?