Taiki Inomata is a student enthusiastic about sports and aspires to arrive first at his school's blue-box gymnasium every day. Unfortunately, his morning smile quickly turns into a frown as he loses again and again to the girl's basketball team leader: Chinatsu Kano. Despite this, Taiki secretly likes his senior, and just the sight of her rekindles his zealous spirit.

With a firm resolve, Taiki plans to declare his love to Chinatsu soon. However, a love confession is far from easy, with Chinatsu potentially having other admirers and Taiki being a complete stranger to her. Can Taiki's youthful love flourish inside the blue box?