For Marine biologist Kim Sung Gyu, his best friend Choi Minhee was a superhero; the woman who cheated death and defied gravity, who stood strong for what she believed in and loved with the entirety of her heart. And for this reason, he lived his life committed to protect her, stand by her side, give light to her kaleidoscopic colors and support her every step of the way; he loved her, unconditionally yet secretly, lest she, yet again, faded away. And then on the day of his birthday, Choi Minhee would tell him that he'd been chosen to give her the gift of life, which would leave him with no choice but to tell her that he loved her.