Koiko Natsume has always strived to be average. She is neither particularly pretty nor ugly, aims for the middle of her class in grades, and makes little to no waves in her interactions. She has an ordinary boyfriend to match her ordinary face, and they share countless ordinary kisses; this is what Koiko believes to be "happiness."

Given Koiko's endeavors toward ordinariness, there is no reason for her to associate with Tsurugi Ninomiya. Tall, handsome, athletic, and smart, he is the antithesis of her credo. That is, until Tsurugi reveals that Koiko's boyfriend has been cheating on her, and discloses one more shocking detail: in all the time he has seen her, she has never once looked happy. With Koiko's "ordinary" world thrown into imbalance, is there any way for an average girl like her to find happiness?