Hayama Kao yearns for an existence that would make people notice her. Even in her final year of middle school when she confessed to the boy she liked for three years, he couldn't even recall her name. Now in high school, she is working as a temporary manager of her school's boys volleyball club against her will. Kao's older brother, an alumnus, currently a teacher and the advisor of the club, placed the responsibility on her shoulders to recruit Kuze Nagisa for the volleyball club if she wanted to quit being the manager. Even though silently observing someone as dazzling as Kiryuu in the club is the only redeeming thing about being the manger, Kao's body aches. She is at her limit and wants to quit being the manager. But no matter how much effort she puts on recruiting Kuze she simply cannot convince him to join. Then one day, she notices something that took her breath away. It was bluer than the sky, even bluer than the sea; it was Kuze Nagisa practicing volleyball all on his own. The blue days start from here!